Dutchman Robin Haase upset German fourth seed Alexander Zverev 5-7, 6-5, 7-5 at the Cincinnati Masters on Wednesday and Wimbledon winner Novak Djokovic cruised into the third round before rain interrupted play.
Haase, who last week kicked off his North American hardcourt swing by reaching the Toronto quarter-finals, converted six of seven break point opportunities to get by world number three Zverev in a match lasting two hours and 25 minutes.
World No 55 Haase improved to a 2-2 career record against Zverev, including victories in their last two meetings.
"We've played four times now," Haase said.
"The first time he literally kicked my ass. ... That was the tournament where he actually came up. And, yeah, since then he's come a long way.
"And now I was there twice physically, mentally and game-wise I was there. And we have to be a little bit lucky, as well, against these top guys."
Haase will face Pablo Carreno Busta in the third round after the Spanish 13th seed beat Bradley Klahn 6-4, 6-4.
Zverev's older brother Mischa was scheduled to face defending Cincinnati champion Grigor Dimitrov but their match was delayed by rain.
Play will not resume before 5:45 p.m. ET (2145 GMT) but the forecast did not look favourable for the rest of the day.
Djokovic, who needs the Cincinnati title to complete his collection of ATP World Tour Masters 1000 trophies, rallied to defeat Frenchman Adrian Mannarino 4-6, 6-2, 6-1.
The 10th-seeded Serb, who has reached the final five times, suffered stomach problems during the match and was tended to by a doctor during the second set.
Djokovic returned to wrap up the second set and raced into a 5-0 lead in the decider before serving out the match. Djokovic will next face either fifth seed Dimitrov or Zverev.
Former champion Marin Cilic of Croatia, competing in Cincinnati for the first time since lifting the trophy in 2016, beat Romanian qualifier Marius Copil 6-7(4), 6-4, 6-4.
Sixth seed Kevin Anderson overcame Jeremy Chardy 7-6(6) 6-2 while Swiss wildcard Stan Wawrinka knocked out Japan's Kei Nishikori 6-4 6-4.
Fourth seed Juan Martin Del Potro had his match against South Korean Chung Hyeon postponed due to rain.
Japan's Kei Nishikori is scheduled to face Swiss wildcard Stan Wawrinka later on Wednesday while Argentine fourth seed Juan Martin Del Potro is due to conclude the evening session with a match against South Korean Chung Hyeon.
Tsurenko stuns defending Cincinnati champion Muguruza
Ukraine's Lesia Tsurenko stunned defending Cincinnati Masters champion Garbine Muguruza with a 2-6, 6-4, 6-4 second-round win over the seventh-seeded Spaniard on Wednesday.
Muguruza, competing in her first tune-up event for the August 27-September 9 US Open, appeared to be heading for a routine victory after rolling through the first set and jumping ahead 3-0 in the decider but Tsurenko had other plans.
Tsurenko stormed back to go ahead 5-4 and sealed the contest on her first match point when a Muguruza forehand from behind the baseline sailed long, giving the Ukrainian world number 44 her first top-10 victory since 2015.
The victory provided some measure of revenge for Tsurenko, who retired hurt just two games into her round of 16 match with Muguruza at this year's French Open.
Next up for Tsurenko is a clash with Ekaterina Makarova as the Russian topped Frenchwoman Alize Cornet 6-2, 6-0.
Joining Tsurenko in the third round is US Open champion Sloane Stephens, who enjoyed a routine 6-3, 6-2 win over German Tatjana Maria.
Stephens, who finished runner-up to world number one Simona Halep in Montreal on Sunday, continued her fine form on the North American hard courts and controlled the tempo throughout her 71-minute match.
Stephens will next face Elise Mertens after the 15th-seeded Belgian earned a 3-6, 6-2, 7-6(1) win over Swedish qualifier Rebecca Peterson.
Also advancing to the third round was Belarusian Aryna Sabalenka, who upset Czech ninth seed Karolina Pliskova 2-6, 6-3, 7-5, and Australian Ashleigh Barty, a 7-5, 6-3 winner over Estonia's Kaia Kanepi.
American Amanda Anisimova had a 5-4 lead on Croatia's Petra Martic in a match that was also halted because of rain.
Top seed Halep, looking to go one better than her runner-up showing in Cincinnati last year, will lead off the evening session with a second-round match against Australian qualifier Ajla Tomljanovic.