The two Australian Open semifinalists last played in Miami a little less than a year ago, when Roddick won only the second of his 17 matches against the current world No. 2. Yet it would be fair to say that losing to Roddick didn't break Federer's stride.
Since last spring, Federer has reached three Grand Slam finals, won the U.S. Open and is camped out one major short of Pete Sampras' record of 14. Roddick struggled with his first significant injury in years, skipped the French Open, made a shockingly early exit in the second round at Wimbledon and went out in the U.S. Open quarterfinals.
Both men arrived here in Melbourne in better shape than they did in 2008. Federer was suffering from a malaise later diagnosed as mononucleosis. The 6-foot-2-inch, seventh-seeded Roddick has shed a few extra pounds that weren't even apparent on a hardworking player who always looked fit. But it's becoming obvious that the newly resculpted Roddick Lite is a player more capable of being a heavyweight.
"He seems like he's back and keen on playing better tennis and putting the effort in to make it happen," iconic Aussie Rod Laver said Thursday.
In past years, Roddick has generally come into Australia at about 200 pounds, according to his longtime trainer, Doug Spreen. He's just five pounds lighter now, but had to lose around 12 or 13 after gaining some weight late last season.
Although Roddick -- with encouragement from his fiancée Brooklyn Decker -- shifted to a healthier diet, this transformation is just as much about conditioning as it is about weight. Roddick bumped up his interval work on the track at home in Austin, Texas, with strength and conditioning coach Lance Hooton, who has worked with a number of elite athletes, including superlative Olympic sprinter Donovan Bailey.
Larry Stefanki, Roddick's new coach, said Roddick regularly ran intervals for 90 minutes after four or five hours on the court and also did more intense core work.
"It was disciplined, severe, killer stuff after you're dead tired," Stefanki told ESPN.com. "I was tired watching him. When you start to get to that pain threshold, situations like this are a cakewalk. It builds so much confidence internally -- 'I've done more work than this guy.' That's critical in the heat."
Roddick looks more like the big-boned whippet he was at 21, when he won the U.S. Open, and told Stefanki he survived the first week of a Slam "without a nick" for the first time in years.
ESPN analyst and U.S. Davis Cup captain Patrick McEnroe knows Roddick as well or better than anyone in tennis and even served as his interim coach briefly last year. Yet even McEnroe said he was surprised at how much of a difference-maker Roddick's weight loss has been.
"It was a great call by [Stefanki] to put it to him that way," McEnroe said. "This has helped his movement, and it'll help him feel better physically over the course of a long tournament."
Roddick looks more at ease in the area that has long been his Achilles' heel, the transition game. When the feet are in the right place, the shots follow, a principle Roddick himself alluded to after dominating much of his quarterfinal match against Novak Djokovic prior to Djokovic's retirement in the fourth set.
"It's a little bit easier to hit the ball when you can reach it," Roddick said.
McEnroe elaborated. "Larry's stressed this, and we've all been saying for years, that Andy should come to net more," he said. "And he did, but he never looked comfortable. You could see him almost panicking, thinking, 'I'm gonna get passed.' Now he looks like he has a lot more balance there.
"The other thing is that when he's being stretched out wide, he's getting more of his weight behind the ball."
Roddick had an easier initial draw than Federer, who had to claw his way back from two sets down against the pesky Tomas Berdych. But while Roddick needed a strong effort to get the better of Djokovic in the quarters, Federer romped over a listless Juan Martin del Potro.
Slitting the jugular in those situations has always been a specialty of Federer's, who never seems to lose focus even when the match is lopsided. "The last couple games are not that much fun" in a rout, Federer admitted. He administered a similar shellacking to Roddick in the semifinals here in 2007, one of Roddick's low points in Grand Slam play.
Despite the fact that Roddick's match against Djokovic ended with a whimper instead of a bang, Roddick's former coach and current ESPN analyst Brad Gilbert called it a mid-career-defining victory. "[Roddick] needed to win that kind of match to get back in the mix," Gilbert said.
Federer also complimented Roddick, saying that Djokovic's retirement took nothing away from the way Roddick played. "Andy forced him," Federer said bluntly. "Andy pushed him to the limits. Hats off to Andy."
Both Roddick and Federer have a somewhat contentious history with Djokovic and seemed pleased at the prospect of playing each other again -- the sixth time they will have met in a Grand Slam semifinal or final. Federer said he was glad to see Roddick back in form, and Roddick said he enjoyed watching Federer defy his doubters and win last year's U.S. Open.
Stefanki said the key for Roddick will be to start at full tilt, holding his ground on the baseline as opposed to backing off it the way he did in the first set against Djokovic. It's an old, bad habit the coach is trying to break, a hangover from Roddick's junior days when he counted more on ball-fetching ability than power. Roddick can sometimes get away with it against a top player if he's serving well, but not against Federer.
"It's very, very important to start strong against Roger," said Stefanki, who saw his previous client, Chile's Fernando Gonzalez, lose in straight sets to Federer in the 2007 Australian Open final. "Roger's a better front-runner than Andy, and Andy's a great front-runner."
These two perennial combatants have great respect for each other. But it's not going to be a lovefest out there Thursday. Roddick may have one Slam trophy to Federer's 13, but there's no such gap in their level of desire. Each man stands in the way of something very, very important to the other.
Bonnie D. Ford covers tennis and Olympic sports for ESPN.com. She can be reached at firstname.lastname@example.org.