SYDNEY - Juan Martin Del Potro launched his comeback from a serious wrist injury with a convincing 6-3, 7-6 (4) win over Sergiy Stakhovsky in the first round of the Sydney International on Tuesday while Canadian Vasek Pospisil beat Andreas Seppi of Italy 6-3, 7-6 (4).

Del Potro, a former U.S. Open champion, is ranked No. 338 after undergoing surgery on his left wrist last year and missing more than 10 months on tour.

He was granted a wild card to enter the main draw in Sydney, where he's the defending champion, but appeared to be fit and sharp in beating 69th-ranked Stakhovsky in 88 minutes. He will face top-seeded Fabio Fognini in the second round.

"These guys are playing all year. It's time to get back on the train again," del Potro said. "This tournament is very special to me."

It was del Potro's second extended layoff with a wrist injury. After capturing his only Grand Slam title at the 2009 U.S. Open, he underwent surgery on his right wrist and was sidelined for eight months.

Pospisil, from Vancouver, had 10 aces in his straight-sets win. He needed 72 minutes to complete the victory.

Bernard Tomic, the 2014 Sydney finalist, needed only 43 minutes to beat Igor Sijsling of the Netherlands 6-1, 6-2.

In other men's first-round matches, seventh-seeded Jeremy Chardy of France had a 6-4, 6-4 win over Sam Querrey and Viktor Troicki of Serbia ousted No. 8-seeded Martin Klizan of Slovakia 6-2, 6-3.

In women's second-round matches, No. 2-seeded Petra Kvitova had a 6-1, 7-5 win over Peng Shuai of China on a day when top-seeded Simona Halep withdrew from the tournament due to gastroenteritis.

Garbine Muguruza of Spain ousted third-seeded Agnieszka Radwanska 3-6, 7-6 (4), 6-2, and her compatriot Carla Suarez Navarro beat sixth-seeded Ekaterina Makarova of Russia 4-6, 6-1, 6-4.

Dominika Cibulkova, the Australian Open finalist last year, was up a set and a break before losing momentum after a rain delay in her match against Australia's Jarmila Gajdosova, who came back to win 1-6, 6-3, 6-4.

Tsvetana Pironkova of Bulgaria advanced when Madison Keys retired from their match when trailing 4-1 in the second set.

Barbora Zhalavova Strycova of the Czech Republic ousted local hope, former U.S. Open champion Samantha Stosur 7-6 (1), 6-2.

In the Hobart International tournament, American Sloane Stephens, the fifth seed, lost to Heather Watson of Britain 6-3, 6-1.

"I didn't do much wrong," Watson said. "I served well, returned well and didn't make many unforced errors and stayed aggressive."

No. 9-seeded Roberta Vinci of Italy beat Annika Beck of Germany, 3-6, 6-3, 6-3 and Japan's Kurumi Nara had a 7-6 (1), 6-4 win over Johanna Larsson of Sweden.

Americans Bob and Mike Bryan, the world's top-ranked doubles combination, suffered a shock 1-6, 7-6 (4), 11-9 loss to unseeded Andre Begemann of Germany and Robin Haase of the Netherlands in the first round of the ATP Tour's Heineken Open in Auckland.

In singles, sixth-seeded Colombian Santiago Giraldo was beaten 6-2, 6-3 in the first round by qualifier Kenny de Schepper of France. Spain's Pablo Carreno Busta beat Croatian teenager Borna Coric 6-4, 6-3.

Diego Schwartzman of Argentina defeated seventh-seeded Guillermo Garcia-Lopez of Spain 6-2, 4-6, 6-1 while qualifier Jiri Vesely downed Thomaz Bellucci of Brazil 6-3, 7-6 (4).

Spain's Pablo Carreno Busta beat Croatian teenager Borna Coric 6-4, 6-3.