LONDON -- In perhaps the biggest heavyweight fight since Lennox Lewis knocked out Mike Tyson to retain the world title in 2002, titleholder Anthony Joshua, the young British star, and Ukraine's Wladimir Klitschko, the regal former longtime world champion and future Hall of Famer, will collide in a once-in-a-generation showdown Saturday.
The fight, which will take place at sold-out Wembley Stadium, has captivated the British public. It's so big that Matchroom Boxing promoter Eddie Hearn was granted permission by the London city government shortly after the fight was announced to add an additional 10,000 seats to bring the stadium capacity to 90,000.
Around the world the bout will be televised in some 140 countries. In an unprecedented move, it will air on rival networks in the United States, both of which will produce their own telecast. Showtime, Joshua's American broadcaster, will have live coverage beginning at 4:15 p.m. ET and HBO, Klitschko's U.S. television partner, will air a taped replay at 11 p.m. ET/PT.
"From a worldwide perspective this has gone from being the biggest fight in British boxing history to one of the biggest fights in world boxing," Hearn said.
This is your ESPN.com Ringside Seat for the big fight:
What's at stake: Anthony Joshua (18-0, 18 KOs) vs. Wladimir Klitschko (64-4, 54 KOs), for Joshua's heavyweight world title and a vacant title
The stakes are as great in this fight as any in boxing. Joshua, 27, will be defending his heavyweight belt for the third time and there is also a vacant title at stake. Both used to be held by Klitschko before he was stunningly upset by England's Tyson Fury in his previous fight 17 months ago.
Fury was quickly stripped of the belt Joshua now holds for failing to immediately commit to a mandatory defense. Then, after twice backing out of a rematch with Klitschko, Fury, who was dealing with numerous personal issues, vacated two other belts. So with Fury out of commission and titleholder Deontay Wilder facing one no-hoper after another -- despite his desire to unify titles -- the Joshua-Klitschko winner will undoubtedly be "the man" at heavyweight and take control of boxing's marquee division.
"We have the young, undefeated champion Anthony Joshua against the longtime ruler of the heavyweight division, Wladimir Klitschko," summed up Bernd Boente, Klitschko's manager.
"I've prepared since Day 1 for this," Joshua said. "(Saturday) is just another stepping stone towards greatness."
Klitschko, the 1996 Olympic super heavyweight champion, is winding down his legendary career at 41, but is by far Joshua's best opponent. If Klitschko scores the upset it would put him back on top of the division he ruled in dominant fashion during a second title reign that lasted for nine and a half years (second longest in division history) from 2006 to 2015 and saw him make 18 consecutive defenses (third most in division history).
A win would also add more history to Klitschko's legacy:
• He can join George Foreman as only the second man over 40 to win a heavyweight title.
• He can become a three-time heavyweight titleholder, joining Evander Holyfield (4), brother Vitali Klitschko, Lennox Lewis and Muhammad Ali.
• He can tie Joe Louis and Floyd Mayweather with the third-most wins in world title fights (26).
• With the first bell, Klitschko will extend his division record by participating in his 29th heavyweight world title fight.
"I'm the challenger again. I feel young, hungry, humble and totally obsessed with my goal to raise my hands again," Klitschko said. "Defeat? I've been there, I've done that. I got up, shook it off and came back stronger. Just a little help (for Joshua) -- there's nothing scary about it."
Joshua has no intention of allowing Klitschko to reach those milestones.
"Klitschko is still here and it's my time to put him out. Put him out for good," Joshua said of the man he once served as a sparring partner for a few years ago. "It's his decision if [he] wants to still fight after (Saturday), but I can cause a massive impact on what he decides to do."
Klitschko is hungry to reclaim his throne and has talked about his "obsession" throughout the buildup to the fight.
"I'm so obsessed with winning," he said. "The belts are very important. I've been attached to these belts for a very long [time]. I had those belts in my past fight, and I'm fighting for these belts in this fight. The only difference is in my last fight they went to the opposite corner. So my goal and obsession is for those belts to land in my corner, in my hands. Obsession is love in extreme shape. I'm in love with my goal."
Yes, 90,000 at Wembley Stadium
The fight was originally looked at for this past December, when it would have likely been at the 20,000-seat Manchester Arena.
It made more sense to delay this a few months and go for a big stadium fight, but even big fights rarely come close to a crowd like the 90,000 expected to fill Wembley Stadium. Klitschko has had many stadium fights in Germany, where he became a star. Those fights regularly drew 60,000-plus fans and this one will dwarf those.
"I know a lot of fans will be watching on TV and in the arena. I've fought in front of huge crowds but 90,000 is my biggest arena," Klitschko said.
In the United Kingdom, where boxing is on a huge upswing, the 2014 rematch between super middleweight titleholder Carl Froch and bitter rival George Groves drew a sold-out crowd of 80,000 to Wembley. Joshua, in his sixth professional fight, opened that card and three years later will headline in front of an even bigger crowd thanks to the added capacity.
"You can't picture it. Fighting in front of 90,000? I'd be lying if I thought I'd say that," Joshua said. "But I wouldn't be in this position if I couldn't handle it. It will be phenomenal. This is why I can't wait. This is a defining fight, everything I dreamed of."
The 90,000 for the fight will match the British record set when Len Harvey won a 15-round decision against Jock McAvoy in a British and Commonwealth light heavyweight title fight at White City in London in 1939.
For perspective, the all-time boxing attendance record is 132,247 for then-junior welterweight champion Julio Cesar Chavez Sr.'s fifth-round knockout of Greg Haugen at Azteca Stadium in Mexico City in 1993.
"In his 19th fight, Anthony Joshua is stepping up to fight a true legend in Wladimir Klitschko and isn't that what boxing's all about? What's sports is all about? Create nights and moments that people will never forget -- 90,000 people in the biggest stadium in the UK," Hearn said.
Klitschko: Ranks third among all CompuBox tracked fighters in jabs landed per round (8.7) and jab connect percentage (30.1 percent).
Klitschko: Opponents land just 5.4 total punches per round against him, which ranks second among active CompuBox tracked fighters, and land just 22.3 percent of their total punches, which ranks 10th.
Joshua: Won 16 of his 18 fights within five rounds and hasn't been past the seventh round in his career.
Joshua: 18-0 (18 KO); only current world champion with 100 percent knockout rate
Too soon for Joshua/Too late for Klitschko?
One of the biggest questions going into the fight is whether Joshua's youth can overcome Klitschko's vast experience. Klitschko has boxed for 27 years between the amateurs and pros. Joshua is 27. Klitschko made 18 title defenses in his second title reign and Joshua has a total of 18 fights.
"I know I have experience. I know that I'm the underdog and I know that he's the young lion," Klitschko said. "I can bounce back. I have done it before."
Joshua, who didn't begin boxing until Klitschko was already into his second title reign, has downplayed the experience factor.
"I'm meant for this. I'm built for this," Joshua said. "Let's say we strip away what you just said, the excitement, the hype and just put us together. Go at it for 12 rounds, get down and dirty. I have the ability to come out on top and that's how I take it. I don't look at it like, 'Oh my God, I'm fighting a guy who has been through it.' I don't look at it that way. I just look at it as I'm going to fight this guy called Wladimir Klitschko and we've got 12 rounds. I simplify it.
"I practice boxing. Long-range jab, jab to the body. I think I'm very capable of hitting someone continuously until they break down. So I think I'll keep on plugging away, Round 6, 7 and I should have him in a bad place. I just have to take the fight and break it down round by round.
"Either he has another fight in him, or this time he's done. I wish him all the best."
On the flipside of the experience is the issue of whether Klitschko, who looked downright old in the loss to Fury, is washed up. Klitschko has addressed that.
"I believe this man has a lot of skills, maybe yes, maybe not he will be the biggest star in boxing," Klitschko said. "I know there are plans to fight Wilder after me. It's good to be young and ambitious, but I believe this fight has a lot of questions. Is it too early for him, too late for me?
"All those questions will be answered -- do I still got it or is it too late? I'm looking forward to his challenge. I have my goal to become three-time world champion and I'm obsessed with it."
Joshua has won all of his fights by knockout and is a tremendous puncher. He has never been down, but he was badly rocked by Dillian Whyte in 2015 in the fight before winning a world title. Klitschko is a devastating puncher as well, with both hands, but has been stopped in three of his four losses and questions about his chin have dogged him for most of his career. Obviously, both guys are capable of scoring a big knockout.
So what about those chins?
"He's got a good chin. How long has he reigned, 10 years? Yeah, he's got a good chin," Joshua said. "You can't be a championship fighter for 10 years if you have a bad chin. That's the thing about the heavyweight division, it takes one shot. All these fighters that we claim have got good chins are the ones who get knocked out by Wladimir, so he must be doing something right. I remember Samuel Peter had a granite chin, but they still end up getting knocked out down the line and they don't go on to do great things. So, regardless of the chin, I think he's got something right that works."
Hall of Fame trainer Freddie Roach, on hand because he is training former junior featherweight titlist Scott Quigg for a featherweight eliminator on the undercard, trained Klitschko for four fights many years ago and advised Joshua to be careful in exchanges "because if he gets caught up in exchanges, and they're both swinging, Klitschko does have knockout power. The left hook's always been his best punch. He has a great left hook. He can't get up caught swinging with this guy. If he trades punch for punch, Klitschko is the better puncher."
Klitschko knows if he lands solid on anyone he can knock them out, but is he fearful of Joshua's power?
"We can both punch well. He's a very strong guy. Do I have fear? I would say I'm a psychologically ill person if I didn't have some fear, but it's a healthy fear," he said. "I am extremely confident and calm. On other side, I'm nervous, which makes me aware, alert and sharp as a knife."
Prediction: Klitschko pulls it out by midrounds knockout.