NEW YORK -- Novak Djokovic rolled to a straight-sets victory to move into the third round at the US Open on Wednesday, fighting not only his opponent but sticky, 85-degree Fahrenheit weather on the hottest day at the tournament so far.
"That's why we train several hours a day in humid, hot conditions so we can be ready for whatever awaits you on court," the second-seeded Djokovic said after a 6-4, 6-1, 6-1 victory in Arthur Ashe Stadium over 76th-ranked Bernabe Zapata Miralles of Spain.
"I still have the hunger," said the 36-year-old from Serbia who owns 23 Grand Slam titles. "I still got it."
Djokovic next faces 32nd seed and compatriot Laslo Djere, whom he beat in their only prior meeting at Belgrade last year.
"It's great for Serbian tennis that we have a matchup in the third round," Djokovic said. "He's definitely one of the top hardest workers out there. Puts a lot of hours into care for his body and trying to build his form. Eventually the results will come for a player like him because he's very, very dedicated."
In the biggest upset of the day, seventh-seeded Stefanos Tsitsipas fell in the second round to 128th-ranked Swiss qualifier Dominic Stricker 7-5, 6-7 (2), 6-7 (5) 7-6 (6), 6-3.
Ending the 4-hour, 4-minute match with a forehand winner that just caught the baseline, Stricker raised his hands and flopped on his back to celebrate his first-ever victory over a top-10 player in only his third Grand Slam appearance.
"I'm just super happy right now," Stricker, 21, told the Grandstand crowd. "I came out and felt good from the first set on. ... I just kept playing high-level tennis."
Closing in on the biggest victory of his career, Stricker was having a terrific time -- so much so that he sang along to Whitney Houston's "I Wanna Dance With Somebody" as it rang out from the stadium speakers during a changeover.
Music often plays during breaks between games at the US Open, and Houston's 1987 hit was the choice while the players sat on the sideline at 5-2 in the fifth set.
Between sips of an energy drink and bites on a snack, Stricker bopped his head and bounced his legs to the beat of the song and then began mouthing the lyrics. He appeared to know all the words.
Tsitsipas, a Grand Slam finalist at the Australian and French Opens, has still never advanced beyond the third round at Flushing Meadows. The Greek player is the second-highest seed to go down on the men's side after No. 4 Holger Rune of Denmark lost to 63rd-ranked Roberto Carballes Baena of Spain.
For Tsitsipas, who won an ATP 250 title in Los Cabos in early August but then went a combined 1-2 at Masters 1000 events in Toronto and Cincinnati, the loss marked another early US Open exit after falling in the first round last year.
"I won't blame it on anything. It's just poor performance after Los Cabos," he said. "I consider myself a good player, and I don't want to be a person that can be beaten easily or I'm giving my opponents easy time on the court against me. I try to make it as hard as I can, and if it doesn't work, it doesn't work. I move on with my life."
Tsitsipas removed his father, Apostolos, as his coach earlier this month but said shake-ups to his team were not to blame.
"By no means I'm supposed to put any blame on any people or any members of my team," he told reporters. "Everything on court is under my control and under my talents, and the way I can play this sport are shown out on the court. If I'm not able to deliver, then I'm not supposed to be doing well."
Tsitsipas had a chance to serve for the match while leading 5-3 in the fourth set, but Stricker stepped up with the break en route to forcing a decider where he consolidated an early break with a hold to love for a 3-0 lead that sent him on his way.
"Such a great day for me, such a great win," Stricker said. "It gives me a lot of confidence and I think it is great to see from my team. We are working hard every day and it is so great to do that."
Elsewhere on the men's side, Dominic Thiem, the 2020 US Open champion, consulted medics and retired soon after dropping a first-set tiebreaker to American Ben Shelton, and French wild card Benjamin Bonzi defeated 28th-seeded Christopher Eubanks 7-6 (6), 2-6, 6-2, 7-6 (7), ending the hopes of an American who made a surprising run to the Wimbledon quarterfinals.
The Associated Press and Reuters contributed to this report.