Cincinnati Open: Alexander Zverev ousted, Novak Djokovic through

Zverev, who suffered a shock defeat to Stefanos Tsitsipas last week in Toronto, saved just one of seven break points in the 5-7 6-4 7-5 reversal.

With the US Open just 12 days away, the German is in a worrying patch of form – especially given his mediocre showings at Grand Slams to date.

Haase complained to the umpire that Zverev was trying to disrupt his serve, but the world number 55 ultimately stayed composed to see out back-to-back wins over his higher-ranked opponent.

"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 meet Spain’s Pablo Carreno Busta in the third round after the 13th seed beat Bradley Klahn 6-4 6-4.

Elsewhere, Wimbledon champion Novak 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.