NEW YORK (AP) The victory came on clay, and it came 4 1/2 months ago.
It also came at a time when Novak Djokovic seemed virtually unbeatable - something that doesn't seem so certain now.
When Jiri Vesely upset the world's No. 1 player in Monte Carlo in April, Djokovic hadn't lost a completed match since November.
Vesely had never beaten a top-10 foe before defeating Djokovic 6-4, 2-6, 6-4. Afterward, Vesely said he didn't believe he could win - until he saw how Djokovic was playing.
''Novak wasn't at his best level, that's for sure, and he made a lot of mistakes from the beginning,'' Vesely said that day. ''That's what gave me a little bit more confidence.''
Coming into the players' rematch in the second round at the U.S. Open on Wednesday, Djokovic hasn't been at his best recently. He lost in the third round at Wimbledon, then after a title in Toronto, fell in the first round at the Olympics, bothered by a left wrist injury.
In the first round at Flushing Meadows on Monday, Djokovic received treatment on his right arm early in a four-set victory over Jerzy Janowicz. He repeatedly winced and shook out the arm, his serves far slower than usual.
After dropping a set in his opening match at a major for the first time since 2010, Djokovic didn't want to talk about what was going on with his arm.
Asked about playing an opponent who defeated him in their only meeting, he ticked off all the reasons that might not be relevant: ''Different surface, different circumstances, best-of-five.''
''Obviously he hasn't played many times on the Arthur Ashe Stadium,'' Djokovic added. ''If you get to play there, it's quite different.''
Vesely, 23, is currently ranked 49th. He's coming off his best performance at a major, a run to the round of 16 at Wimbledon that included another win over a top-10 player in Dominic Thiem.
Djokovic's scouting report on the 6-foot-6 Vesely: ''Big game, a big serve, big forehand, and moves well for his size.''
But big serves are usually swallowed up by Djokovic's stellar return game - and he believes the roof structure on Ashe that cuts down wind aids him even more.
''Conditions are quite suitable to my style of the game,'' he said. ''Hopefully I'll be able to slow his serve down a little bit and then take it from there.''
Other matches to watch on Day 3 of the U.S. Open, when the second round begins:
The last two matches on the Grandstand will feature two U.S. women facing each other.
Eighth-seeded Madison Keys meets 16-year-old Kayla Day, the youngest player in the draw. Day, ranked 374th, got into the tournament as the winner of the USTA Girls' 18s National Championships. She was leading 6-2, 4-2 in the first round when her opponent, Madison Brengle, retired with an arm injury. Brengle, at No. 50 in the world, had been the highest-ranked opponent Day has faced in her young career.
Day followed in the path of CiCi Bellis, who as a 15-year-old in 2014 won the same national title and reached the second round at the U.S. Open. Now 17 and a qualifier, Bellis faces 49th-ranked Shelby Rogers on Tuesday. Rogers was a surprise quarterfinalist at the French Open this year.
Fourth-seeded Rafael Nadal met his second-round opponent, Andreas Seppi, just over three weeks ago at the Olympics. In his second match back after a 2 1/2-month layoff, Nadal won that day 6-3, 6-3.
Nadal and Seppi play the nightcap on Ashe. Fellow Spaniard Garbine Muguruza, the French Open champ, faces 48th-ranked Anastasija Sevastova to open the session.
DOUBLE NO. 2
Second-seeded Angelique Kerber meets Mirjana Lucic-Baroni, who two years ago upset second-seeded Simona Halep in the third round.