Wins for Kyrgios, Thiem, Halep and Muguruza at Ohio tournament.
Del Potro pleased with his game after victory over Berdych at Cincinnati
Juan Martin del Potro made a winning return to the Cincinnati Open on Tuesday when the Argentine ground out a 3-6, 7-6, 6-0 victory over 10th-seeded Czech Tomas Berdych to reach the second round on Tuesday.
Del Potro, 28, back in Cincinnati after a four-year absence from the US Open warm-up event, powered down 17 aces to rally past Berdych after he surrendered the opening set following a listless start.
Berdych found his rhythm early in the match and broke Del Potro for a 3-1 lead and did not lose a point on his powerful serve until the 10th game.
But as Del Potro, a semi-finalist at the tournament in 2012 and 2013, worked his way back into the match, Berdych slowly began to lose confidence and failed to win a single game in the deciding set.
From Graham Caygill:
"During the second set, in the end, I played my best tennis," 2009 US Open champion Del Potro said. "I hit so sure with my forehand. I made good serves and I took all my chances to win.
"Mentally, I was strong enough to keep fighting and I think he got down after losing that second set. Then, when I broke his serve early in the third [set], my game started improving and I played much better than him."
Del Potro advances to meet American qualifier Mitchell Krueger in the second round.
Australian Nick Kyrgios also opened his campaign with a welcome victory as the world No 23 beat Belgian ninth seed David Goffin 6-2, 6-3 in the afternoon heat to reach the second round.
Other than in the first game when he had to climb out of a 0-40 hole, Kyrgios experienced few problems on serve and even secured three breaks against Goffin, who had to take a medical time out for a knee injury during the match.
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"He obviously wasn't at 100 per cent today but you know I'm not at 100 percent either, so it was a bit of a battle," said Kyrgios, who has struggled with an array of injuries throughout the season.
"But I served well at crucial moments. I'm feeling okay. I think as long as I can keep putting in performances like these and being able to compete I think I'm okay."
In other action, third seed Dominic Thiem of Austria was barely tested in his 6-3, 6-2 second-round win over Italy's Fabio Fognini, while Jack Sock beat fellow American Tommy Paul 6-3, 6-3 to reach the round of 16.
Earlier in the day, big-serving Canadian Milos Raonic, the sixth seed, announced his withdrawal from the tournament due to a lingering left wrist injury.
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Win for Halep
World No 2 Simona Halep coasted into the third round of the Western & Southern Open in Cincinnati with a straight-sets win over Taylor Townsend.
The Romanian, given a first-round bye, came through 6-4, 6-1 in one hour and seven minutes against the American qualifier.
Johanna Konta is also through to the third round after seeing off Kiki Bertens.
The seventh seed advanced in straight sets, 6-3, 6-3, and looked in impressive form with both her forehand and backhand as she forced 10 break points, converting four of them.
Konta will now await the winner of the second round tie between Frenchwoman Alize Cornet and 11th seed Dominika Cibulkova.
Cornet defeated Catherine Bellis of the United States in three sets, 7-6, 3-6, 6-2 in a first-round tie.
No 9 seed Venus Williams booked her place in round two with a straight-sets 6-2 6-0 win over fellow American Alison Riske.
French Open champion Jelena Ostapenko, though, is out after the Latvian No 12 seed lost 6-4, 6-2 to Aleksandra Krunic of Serbia.
Cibulkova, the 11th seeded Slovakian, needed three sets to defeat Ana Konjuh of Croatia, the world No 11 eventually coming through 5-7, 7-5, 6-2 following almost two-and-a-half hours.
Poland's No 10 seed Agnieszka Radwanska went down 6-4, 6-4 to Julia Goerges of Germany, while 15th seeded Latvian Anastasija Sevastova came through 3-6, 6-4, 6-2 against Shuai Peng of China.
Australian qualifier Ashleigh Barty won 6-4 6-4 against American Varvara Lepchenko to set up a second-round date with Williams.
Spanish fourth seed Garbine Muguruza wasted no time in advancing to the third round with a 6-2, 6-0 win over Brazilian qualifier Beatriz Haddad Maia, while Ekaterina Makarova was almost as dominant in beating Barbora Strycova 6-4 6-1 in their first-round tie.
Wildcard Sloane Stephens advanced to the second round with a 6-4, 7-6 win over Lucie Safarova, while there were also first-round wins for Elena Vesnina and qualifier Francoise Abanda.