Roger Federer began his pursuit of an eighth title at the Western & Southern Open in Cincinnati, Ohio, with a win on Tuesday, but another former number one, Serena Williams, bowed out in her second-round match.
Federer, the number two player in the world, struck 12 aces and won 79 per cent of his first serves in defeating Peter Gojowczyk of Germany 6-4, 6-4. He also saved all five of the break points he faced in the match, the first between the two players.
The second-seeded 37-year-old is playing for the first time since losing in the Wimbledon quarter-finals to Kevin Anderson. The world number two will face 50th-ranked Leonardo Mayer of Argentina in the second round.
Williams, holder of 23 grand slam titles, has been struggling to return to the game since becoming a mother last year in September. She roared past Daria Gavrilova 6-1, 6-2 in the first round of the Western & Southern on Monday. But just a week ago she lost to Johanna Konta 6-1, 6-0 in San Jose, California, before withdrawing from last week's Rogers Cup in Montreal.
Her 6-3, 2-6, 6-3 loss to 6th-ranked Petra Kvitova of the Czech Republic on Tuesday dashed her hopes of winning a third title in Cincinnati.
In other matches Tuesday, Stefanos Tsitsipas of Greece played his debut at Cincinnati, a 7-5, 6-3 loss to 11th-seeded David Goffin of Belgium, a finalist in Cincinnati last year. On Sunday, his 20th birthday, he lost to Rafael Nadal in the final of the Rogers Cup in Toronto after beating four top-10 players in the Masters 1000 event.
Nick Kyrgios of Australia, the 15th seed, also got through to the second round, downing American Denis Kudla 6-7 (7-2), 7-5, 7-6 (7-9).
Earlier Tuesday, Milos Raonic of Canada dispatched Dusan Lajovic of Serbia 6-3, 6-3 in less than an hour and Kevin Khachanov of Russia defeated Albert Ramos-Vinolas of Spain 2-6, 6-3, 6-2.
Marius Copil of Romania also won his match over Philipp Kohlschreiber of Germany 6-4, 6-2 to advance to the round of 32, and Hyeon Chung of South Korea out-lasted Jack Sock of the United States 2-6, 6-1, 6-2.
World number one Nadal pulled out of the tournament, one of the North American hard-court events leading up to the US Open, on Sunday immediately after his victory in the Rogers Cup in Toronto.
The women's draw also saw former champion Victoria Azarenka of Belarus crash out 6-4, 7-5 to Caroline Garcia of France. Garcia, the sixth seed, came from a break down in each set to dismiss the two-time Australian Open champion.
Top seeds Simona Halep, Caroline Wozniacki, Sloane Stephens and Angelique Kerber are scheduled to play their first matches in the tournament on Wednesday.