Johanna Konta began her bid for the Cincinnati Open women’s title with a straight-sets win over Croatia’s Donna Vekic.
Having received a bye from round one, the world No 13 defeated her opponent 6-2 6-3 to set up a last-16 meeting with Agnieska Radwanska.
Having reached the quarter-finals of the Olympic singles tournament before losing to Angelique Kerber, Konta is attempting to reach her second final of the season.
She was rarely troubled by Vekic and the 25-year-old will now take on Poland’s Radwanska for the first time.
Elsewhere, Serena Williams will lose her place as number one to Angelique Kerber if the German wins the tournament and she enjoyed a 6-0 7-5 win over France’s Kristina Mladenovic.
Williams has led the rankings for 183 weeks but is missing the event because of an inflamed shoulder.
Kerber said: “It’s not on my mind. If the time is ready and I can reach number one, of course it will be amazing. Still, it’s for me still a long, long way to get there.”
Romanian third seed Simona Halep defeated Germany’s Annika Beck 6-3 6-1 while and fourth-seeded Garbine Muguruza of Spain beat American Coco Vandeweghe 7-6 (7-4) 6-2.
In the men’s draw, Rafa Nadal – beaten in the bronze medal match at the Rio Olympics by Kei Nishikori – beat Uruguay’s Pablo Cuevas 6-1 7-6 (7-4).
The Spaniard, who won doubles gold with Marc Lopez, said: “I think I played well. I played a good match against a tough opponent in the first round for me for sure.
“After coming from Rio and after the marathon that I had, it’s a very important victory for me. So I’m very happy.”
Nadal will play Croatia’s Borna Coric next, a 7-6 (7-2) 4-6 7-6 (8-6) winner over Nick Kyrgios, who vented his frustrations by smashing three rackets in quick succession during a break between games.
Second-seeded Stan Wawrinka of Switzerland also advanced, beating American Jared Donaldson 2-6 6-3 6-4.
Canada’s Milos Raonic, the fourth seed, beat American John Isner 7-6 (7-5) 7-6 (7-5) and Nishikori topped Russia’s Mikhail Youzhny 6-3 6-2.
Tomas Berdych beat Spain’s Marcel Granollers 6-3 7-6 (7-4) while seventh-seeded Jo-Wilfried Tsonga had a 7-6 (7-5) 7-6 (7-3) win over American Reilly Opelka.