BRISBANE, Australia (AFP) — A pain-free Serena Williams sent an ominous warning to her rivals as she crushed fellow American Varvara Lepchenko 6-2, 6-1 in the first round of the Brisbane International yesterday.

Third-seed Williams, 31, pulled out of an exhibition tournament in Thailand last week amid concerns she had not fully recovered from a recent foot surgery.

But she looked in great touch against Lepchenko, who was never able to trouble Williams after squandering five break points in the opening game.

The 15-time grand slam winner quickly found her groove as she romped away to win in 59 minutes.

"My foot didn't hurt today," a relieved Williams said. "I was a little nervous, but I was completely fine.

"I was excited to get an early start so just in case I did have any pain I could have tomorrow off, but everything was fine."

Williams entered the tournament as firm favourite after a stellar second half of 2012, during which she won seven titles, including Wimbledon, the US Open, the WTA Championship and the Olympics.

"I love winning, and I feel like as long as I'm able to win some matches and do well, I'm really motivated to keep going," she said.

"I just love being out there. I think going through what I went through a year and a half ago (when she suffered from severe foot injuries) really just made me realise that I get to do this and have fun."

Former Wimbledon champion Petra Kvitova got her campaign off to an impressive start when she downed Spaniard Carla Suarez Navarro in straight sets.

Kvitova, the sixth seed, cruised through the first set and opened a 5-3 lead in the second, but was forced to hold off a Suarez Navarro fight back to win 6-3, 6-4 in 90 minutes.

The tall left-hander had a stellar 2011 when she broke through to win Wimbledon along with five other WTA titles on her way to a career-high ranking of number two, having started the year at 34.

Poland's Urszula Radwanska defeated Tamira Paszek of Austria 2-6, 6-0, 6-2, while Australian wild card Jarmila Gajdosova upset Italy's world number 16 Roberta Vinci 4-6, 6-1, 6-3 to set up a clash with second-seed Maria Sharapova.

Slovakia's Daniela Hantuchova progressed after seeing off Lourdes Dominguez Lino 7-5, 6-2.

Hometown favourite Samantha Stosur plays her first match tonight against Sweden's Sofia Arvidsson, with the top two seeds Victoria Azarenka and Sharapova not playing until tomorrow.

Meanwhile, Serena's sister Venus Williams rallied to defeat Chanelle Scheepers 4-6, 6-2, 6-3, before Kevin Anderson levelled the tie for South Africa with a 7-6 (0), 7-6 (5) win over John Isner as the United States claimed a 2-1 victory over South Africa at the Hopman Cup mixed team competition in Perth, Australia, yesterday.

The US clinched the tie by winning the mixed doubles 6-3, 6-2.

Venus Williams took time to settle against an opponent who rallied well and hit the ball deep. But after conceding her serve at love to leave Scheepers serving for the first set, the American looked increasingly comfortable and aggressive.

After taking the second set when her opponent double-faulted, she then swept to a 4-0 lead in the third on her way to closing out the match.

Isner held the only break point of the first set for a 4-2 lead but missed his return. In the second set, Isner fought off three break points at 3-2 and another at 4-3, but again fell short in the tiebreaker.

Williams was playing for the first time since winning the Luxembourg event in mid-October and was satisfied with her performance.

"I was just trying to find some rhythm out there," Williams said.