Dominant Serena Williams getting better and fitter with every match

It was a dominant display from the world No 1, who dropped just three points on her first serve while winning more than half of the points on Kvitova's service.

Williams is chasing a fifth title at Melbourne Park and ominously for her rivals said afterwards she was already nearing peak form and fitness. "I thought was a little bit better than my match in my first round," said Williams, who had come into the tournament under a fitness cloud after limping through her defeat against Elena Dementieva in the final at Sydney last week.

"I felt like I was moving better and I had better energy. I just felt all around a lot better. I don't think I'm that far (from full fitness) and I felt like I could have actually played a lot better."

Williams will next play 32nd seed Carla Suarez Navarro, who beat Germany's Andrea Petkovic 6-1, 6-4.

Sixth seed Venus Williams, who is chasing her first Australian Open title at the age of 29, claimed her second consecutive straight-sets win as she was similarly untroubled by Sybille Bammer 6-2, 7-5.

It was the second left-hander Williams has played and she will meet another in the last 32 after unseeded Australian Casey Dellacqua defeated Karolina Sprem 7-6 (7/4), 7-6 (8/6) in the final match.

Ana Ivanovic, the former world No 1, continued her disappointing grand slam form since winning the 2008 French Open as she was bundled out by 36th-ranked Gisela Dulko 6-7 (6/8), 7-5, 6-4. It is the seventh major in succession the Serbian has failed to get past the fourth round and she admitted her growing frustration at the early exits.

"It hurts, I must say," she said. "I think I just have to be patient. It will take some time. I do feel better on the court. I feel like my old self.

"There are still some areas that are not there for me to rely on when I need them the most. Some matches it's there, some not."

The fourth seed from Denmark, Caroline Wozniacki, played for the second consecutive day but showed no ill-effects with a trouble-free 6-3, 6-1 win over Germany's Julia Goerges.

Belarus' Victoria Azarenka reached the third round of a grand slam for the 11th consecutive occasion with a simple 6-4, 6-0 win over Stefanie Voegele.

Agnieszka Radwanska, the tenth seed, and 17th seed Francesca Schiavone both had straight-sets wins and will now meet in the third round.

Australia's top hope Samantha Stosur (13) will avoid a seed in the next round, however, after the Queenslander beat Kristina Barrois 7-5, 6-3. Unseeded Italian Alberta Brianti lies in waits after she upset Sabine Lisicki, the 21st seed 2-6, 6-4, 6-4.

Other seeded players to progress were China's Na Li (16), Daniela Hantuchova (22) and Shahar Peer (29).