Top seed Alexander Zverev of Germany advanced to the last eight of the Rio Open on Wednesday with a 7-6 (1), 7-6 (6) victory over Kazakhstan's Alexander Shevchenko.

Zverev took the first set in 72 minutes on the outdoor clay of the Jockey Club Brasileiro before falling behind 2-5 in the second.

The world No. 2 saved two consecutive set points from Shevchenko and then rallied to close out the second set and prevail in two hours and 28 minutes. The result sets up a quarterfinal meeting with Argentina's Francisco Comesana.

"Generally, I thought it was a pretty good match. The conditions are not easy here. It's hot, humid. You go to your limits sometimes physically," Zverev said. "I thought he played a very good match, so I'm happy with the win and definitely happy with the improvement from yesterday."

The result came a day after Zverev needed more than two hours to account for China's Buyunchaokete 7-6 (4), 6-4.

The 27-year-old admitted he was struggling to capture his best form in Rio de Janeiro's sweltering heat and humidity.

"I was in bad shape physically and really struggled to breathe," Zverev said. "The air is very heavy here. Very, very humid. I caught myself then afterwards and obviously happy I didn't have to play a third set."