Tennis - Del Potro strolls to Sydney title, Isner aces Auckland

Argentine Juan Martin Del Potro served notice of his strong form ahead of the Australian Open when he crushed defending champion Bernard Tomic 6-3 6-1 in the final of the Sydney International on Saturday.

The 2009 U.S. Open champion simply overpowered the talented but inconsistent Australian on Ken Rosewall Arena, bringing the one-sided contest to a close with a booming service winner after 53 minutes.

Seeded fifth at Melbourne Park, the 25-year-old looks to be approaching the sort of intimidating form that secured him his greatest triumph at Flushing Meadows before a wrist injury nearly ended his career.

Playing near faultless tennis, Del Potro served with venom and unleashed powerful forehands and backhands that forced a string of errors from the overwhelmed Tomic.

Tomic, who faces world number one Rafa Nadal at the Australian Open next week, admitted Del Potro had been "too good" when the pair shook hands at the net.

American John Isner earlier claimed his second Auckland Open title with a 7-6(4) 7-6(7) victory over an inspired Lu Yen-Hsun in a tight final in New Zealand.

While Lu ultimately came up short in his first final, Spanish qualifier Garbine Muguruza hammered Klara Zakopalova 6-4 6-0 in hers to clinch a maiden WTA title at the Hobart International.

Japan's Kei Nishikori was also a winner on Saturday when the lucky loser finalist beat world number seven Tomas Berdych 6-4 7-5 to win the Kooyong Classic exhibition tournament.

In Auckland, Isner crashed down 23 aces but it would take more than his big serve to corral the Taiwanese, who put on a brilliant display of shot-making in his first ATP final.

Lu, number 62 in the world, stunned David Ferrer to end the Spaniard's three-year reign as champion in the semi-finals but Isner held his nerve when it mattered to edge two tiebreaks and avoid another upset.

"I played exceptionally well today and I needed every bit of it to come out on top," said the American, who is seeded 13th for Melbourne Park and, like Del Potro, will meet a qualifier in the first round.

"I'm very happy to put my name on this trophy along with my coach Michael," said Nishikori, who lost to Berdych earlier in the week and replaced Richard Gasquet after the Frenchman pulled out on Friday.