CINCINNATI, OHIO - Unseeded German Jan-Lennard Struff resisted a Stefanos Tsitsipas fightback while Serbian teenager Miomir Kecmanovic beat fifth-seed Alexander Zverev as two of the bigger upsets on Wednesday at the Cincinnati Masters.

Struff, who has yet to win an ATP singles title in his decade-long career, was on top for most of the match against the 21-year old Greek.

He served for the match in the second set but Tsitsipas managed to stay alive by taking the set on a tiebreak.

However, the German refused to give up and sealed the 6-4 6-7(5) 7-6(6) victory to set up a third round meeting with ninth-seed Daniil Medvedev, who beat France's Benoit Paire 7-6(2) 6-1.

"I had a chance to serve it out at 6-4 5-4 but he broke back and that's the quality he has," Struff said.

"The quality I had today was coming back from that, the chance to win the match in two sets, then at 6-3 in the (third set) tie-break and then from 6-6.

"He was playing very well. I was telling myself 'I have to go for it, otherwise I won't win'.

"I've been working hard with my team on my fitness and it's all finally paying off and I'm playing with greater consistency." -Reuters