US Open runner-up Alexander Zverev overcame a slow start to launch his French Open challenge with a 7-5 6-2 6-4 victory over Austrian Dennis Novak on Sunday.
US Open runner-up Zverev, who had not played on clay since last year, trailed 4-1 in the opening set before he turned the screw on Court Philippe Chatrier, whose roof remained open despite a light drizzle.
"Close the roof!" screamed one of the few spectators during the second set.
It made Zverev smile but did not affect the German's focus as he set up a meeting with either France's Pierre-Hugues Herbert or American qualifier Michael Mmoh.
"I didn't play any claycourt before this, it's my first one (this year) and it was not easy. It was rainy and cold, I needed to get used to it, said the 23-year-old Zverev.
"He's a player who is good on this surface. He grew up with (fellow Austrian) Dominic Thiem. All they did was play on this surface."
Addressing his critics, Zverev added: "Some say that I don't do well at Grand Slams, I'm proving them wrong this year. I'm hoping for a deep run here."
Zverev, who never made it past the last-eight at Roland Garros, reached the semi-finals at the Australian Open before losing to Thiem in the US Open final earlier this month.
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