MASON, Ohio (AP) -- Roger Federer advanced to the third round of the Western & Southern Open with a 6-4, 6-4 victory against Peter Gojowczyk on Tuesday.
It was Federer's first Cincinnati appearance since winning his tournament-record seventh championship in 2015. After a first-round bye, Federer extended his Cincinnati winning streak to 11 matches since losing to Rafael Nadal in the 2013 quarterfinals.
The second-seeded Federer, refreshed from a month off after losing in the Wimbledon quarterfinals, became the tournament favorite when Nadal withdrew on Sunday night.
Karolina Pliskova and Nick Kyrgios also advanced Tuesday in early tournament action.
Pliskova moved into the second round by snapping a seven-match losing streak against Agnieszka Radwanska with a 6-3, 6-3 win.
"It means a lot because it was against her, and, like, you know, I never beat her," Pliskova said. "We played so many times. I think I always played her at her best level the matches before, so it was always tough."
Kyrgios, a finalist last year in Cincinnati, overcame physical problems to fight off qualifier Denis Kudla for a 6-7 (2), 7-5, 7-6 (9) victory.
"This year has been tough," Kyrgios said. "I started the year very well. Then, obviously, I hurt my elbow. Then I had an ongoing hip injury. We have been definitely thinking about the options with my hip. You know, there is only so much you can do before you have to, you know, I guess, get surgery or something like that. You know, right now I'm just managing it."
No. 11 seed David Goffin advanced with a 7-5, 6-3 win over Stefanos Tsitsipas, and Leonardo Mayer became the first player to reach the third round on the men's side with a 7-6 (7), 6-4 victory over 16th-seeded Lucas Pouille.
Australian Open semifinalist Hyeon Chung won the last five games to beat Jack Sock 2-6, 6-1, 6-2. Sock has lost eight straight matches since winning in Rome on May 13.
Two-time Cincinnati semifinalist Milos Raonic advanced with a 6-3, 6-3 win over qualifier Dusan Lajovic. Robin Haase also made it to the second round, defeating Filip Krajinovic 4-6, 6-2, 6-3.
Sixth-seeded Caroline Garcia reach the third round with a 6-4, 6-5 win over wild card Victoria Azarenka. Elise Mertens scored a 6-4, 6-2 first-round win over Magdalena Rybarikova. Ashleigh Barty stopped wild-card Marketa Vondrousova 6-3, 7-5.
Maria Sakkari upset Indian Wells champion Naomi Osaka 6-3, 7-6 (8). Ekaterina Makarova cruised past qualifier Ana Bogdan 6-3, 6-2.