Title holder Alexander Zverev on Thursday defeated Frenchman Hugo Gaston 4-6, 6-2, 7-5, securing his spot in the quarter-finals of the Hamburg Open. Zverev initially struggled and lost the first set after 47 minutes. He contested a point when he thought the ball had double-bounced in Gaston’s court. “I was on the verge of losing my nerve completely once or twice. You stopped me from doing that,” the Hamburg native said after the match, thanking the home crowd for their support. Zverev managed to rally and win the second set. In the third set, there was some debate when Zverev initially thought…