Jannik Sinner and Aryna Sabalenka got their title defences off to smooth starts as they powered into the third round of the ATP-WTA Cincinnati Open on Saturday.

The men's and women's top seeds, each ranked number one in the world, were both competing for the first time since Wimbledon – where Sinner lifted the title and Sabalenka bowed out in the women's semi-finals.

Sinner crushed Colombian Daniel Elahi Galan 6-1, 6-1 in steamy afternoon weather while Sabalenka beat 2023 Wimbledon champion Marketa Vondrousova 7-5, 6-1 under the lights of the night session.

Sabalenka won the opening set in 54 minutes, but the second set was more of a grind than the score suggested as she saved five break points for a 4-1 lead and recovered from 0-30 down in the final game before securing the win.

"She pushed me to the limit. If you lose focus even a little bit it can cost you a set. I had to fight for every point against her," said Sabalenka, who next faces Britain's Emma Raducanu, a 6-3, 6-2 winner over Olga Danilovic.

Meanwhile Sinner outclassed Colombia's Galan with 17 winners and just four unforced errors.

Sinner won the opening five games in 15 minutes as he allowed his 144th-ranked opponent, who came through qualifying, little breathing room.

The victory in 59 minutes was the fastest of Sinner's ATP career, beating his previous quickest by one minute.

"Today I was finding my spots but there is still a little room to improve. For a first match it could not have gone better," said Sinner.

After snapping up the first set Sinner broke to start the second before Galan clawed out a hold in a seven-minute game in which he fought off five break points.

But it was only a momentary reprieve. Sinner fired three aces to hold for 3-1 as he roared away again for the victory. (AFP)