NEW YORK -- Tested for the first time at this U.S. Open, Novak Djokovic barely passed -- winning a rousing 30-point tiebreaker.
Alexandr Dolgopolov can be a daunting opponent. He has won only four more matches than he has lost at the ATP World Tour level, but he's quirky, hard to read and a fantastic shot-maker.
Monday, Dolgopolov threw in an extra element: the slice.
He sliced the backhand, cross-court and down the line. He sliced the forehand -- even using it to try to pass Djokovic. For 76 minutes, this seemed to confuse the world's No. 1 player, who used to have a problem with the low-energy ball to the forehand.
Finally, after surviving four set points against him, Djokovic cashed his sixth set point to take the first set, 16-14. Dolgopolov, after three straight slices, tried to flatten out a forehand, and it sailed long. The fans at jam-packed Louis Armstrong Stadium leaped to their feet and applauded. Djokovic, ever the showman, pointed his finger at his ear -- and they roared even louder. Afterward, both players looked exhausted but had bemused looks on their faces.
Djokovic settled down to win 7-6 (14), 6-4, 6-2.
"It was very tricky conditions," Djokovic said in his on-court interview. "He was playing a lot of low balls, a lot of slice. I was confused on the court. But it was really exciting.
The Serb is 61-2 for the season, one of the greatest starts in history. Djokovic has been remarkably consistent this year; the last time he lost to a player ranked outside the top 20 (Dolgopolov is at No. 23) was 10 months ago, when he fell to Michael Llodra in Paris.
Djokovic meets Janko Tipsarevic in an all-Serbian quarterfinal Wednesday. It's the first time in the 43 years of the Open era that two Serbs have reached the quarters of a Grand Slam.
"We are great friends," Djokovic said. "This is the first time we have played in a Grand Slam. There's going to be one Serbian in the semifinals, which is great for our country.
"It's not going to be easy playing him, but it's the quarterfinals and somebody has to win."
2. Thanks for the memories: Rafael Nadal never, ever forgets a loss.
At the end of a detailed assessment of his play here, Nadal referenced his fourth-round opponent, Gilles Muller, a 28-year-old from Luxembourg.
"I already lost with him in Wimbledon 2005," Nadal said. "This year was tough, especially tough, two sets against him in Wimbledon. He's a very aggressive player. Fantastic serve. I have to move him. Probably his movements are the worst thing, but the rest of the game can really be dangerous."
Muller, who extended Rafa to tiebreakers in those first two sets at Wimbledon 2011, is ranked No. 68 among ATP World Tour players and is 13-7 for the season.
3. Murray seeks revenge: After Andy Murray reached the finals of the Australian Open, he found himself in "a pretty bad place."
He lost his first match in Rotterdam to Marcos Baghdatis. Then things really fell apart. Donald Young, then ranked No. 143 in the world, took Murray down in straight sets at Indian Wells. Later in March, Murray exited Miami when he lost his first match to Alex Bogomolov Jr., then ranked 118.
A few weeks ago in Cincinnati, Murray avenged the Miami loss by sending Bogomolov home. Is he the kind of guy who wants revenge?
"Yeah," said Murray, smiling. "Yeah, I do.
"It was a tough part of the year for me. It's more sort of, not so much revenge against Donald, it's more for the situation I was in there and making sure I can kind of move on. Winning against Bogomolov in Cincinnati was very, very important for me. The match against Young won't be any different."
Mr. Young, consider yourself warned.
4. Fed hardly shy -- or retiring: It's been a physically rough U.S. Open by any standard. No fewer than 14 players have retired from matches here -- a new record. On Sunday, even venerable Bud Collins succumbed, pulling out with a torn tendon to his patella, an injury suffered in a fall in his hotel.
Roger Federer, asked his opinion on the topic, took his professional peers to task for unprofessional behavior.
"For me, it is shocking to see so many retirements," Federer said. "I have never retired in my whole life except once when I played against [James] Blake in Paris, but I didn't even walk on to the court. For me, it doesn't matter how bad I'm feeling, I will be out there and giving it a try because you never know what's going to happen.
"Look, every player feels different. It's unfortunate it happens for the fans, I guess."
Greg Garber is a senior writer for ESPN.com.