Rafael Nadal extended his unbeaten run over Frenchman Richard Gasquet to 15 to reach the Cincinnati Open third round.
The Spaniard, 31, who has not lost a set to Gasquet since 2008, won 6-3 6-4 on Wednesday.
Roger Federer's withdrawal from the tournament means on Monday Nadal will return to world number one for the first time since July 2014, taking over from Andy Murray who is also injured.
Meanwhile, Alexander Zverev's 10-match winning streak ended with defeat by unseeded American Francis Tiafoe.
Zverev, 20, has moved up to seventh in the world rankings following victory over Roger Federer in Montreal.
But he lost 6-4 3-6 4-6 to 19-year-old Tiafoe, the world number 87.
Zverev arrived in Cincinnati having won back-to-back titles in Washington and Montreal, and he will start among the favourites when the US Open gets under way on 28 August.
"I'm not a machine. I'm tired. There was no hiding it. There's a physical limit to all of us and I've reached that now," Zverev admitted.
"This match is already forgotten. But it's something that's normal. It happens to all of us."
Nadal, who won a record 10th French Open in June, will next face fellow Spaniard Albert Ramos-Vinolas.
"I work every day to play better. It's obvious that was an important start for me, a good one."
