MELBOURNE (AFP) - Seven-time grand slam singles champion Venus Williams was in vintage form on Thursday, cantering past Lauren Davis in straight sets at the Australian Open and saying her vast experience was paying dividends.

The 34-year-old American, seeded 18, is now on a 7-0 run after winning the lead-up Auckland Classic as she works to reach the second week of a grand slam event for the first time since Wimbledon in 2011. She has lost just one set during that time, to world No 8 Caroline Wozniacki in the New Zealand final.

Her younger sister, top seed Serena Williams, meanwhile almost sleepwalked to an upset before finding her mojo and bulldozing former world No. 2 Vera Zvonareva 7-5, 6-0 to make it to the third round.

Chasing her sixth title at Melbourne Park, 33-year-old berated herself for a "passive" early effort when she had to save two set points against the Russian.

Williams, whose world No. 1 ranking will be under threat is she does not win the tournament, did not rouse herself until the ninth game, when she was on the brink of going down a set.

"She started out really well, she was really aggressive and I was a little too passive," said Williams, who would take her total Grand Slam singles tally to 19 with another Australian title.

"Once I got down I thought 'Serena, you've done so well here you've got nothing to lose, just have fun and enjoy yourself' - then I started to play a lot better."

Williams faces a tricky third-round match against Spanish world No. 24 Garbine Muguruza, 21, one of the new generation coming through in women's tennis.

A buoyant Venus said after beating fellow American Davis 6-2, 6-3 to make the third roun: "I'm hitting the ball a lot like how I want to. Some points you play well and some not as well. I'm just continually trying to be as consistent as I can on the court and still play consistent while taking risk as well."

Williams, who has long battled illness and injury, will next meet either Czech Tereza Smitkova or Italy's Camila Giorgi.

She has been playing grand slam tennis since 1997 and said the experience was a crucial part of her game now she was getting older.

"Honestly, I think I understand the game a lot more," she said.

"Even when I'm not playing as well, I think I'm able tactically to be more strategic than even, let's say, the Venus of 2000.

"So I think there is a big difference.

"I watched some old matches, and I'm like, 'Wow, if I could have been more strategic I could have won this match a lot easier'.

"So I think strategically it's more helpful, even if I am not on top of my game. I understand things a lot more. So that's one of the beauties of continuing to play as you get a lot of the years under your belt."

Against Davis, Williams lost serve once in each set but from start to finish she was on her game, attacking and moving forward the whole time, blasting 18 winners in total and finishing eight points at the net.

While she is targeting the second week of a Slam for the first time since Wimbledon in 2011, she said that ultimately all she cared about was winning titles.

"For me it's about titles, so no matter what the title is for me, to the finals is the same thing as the third round if I didn't win," she said.

"For me, it's about hopefully trying to take titles home."