Serena Williams stormed past Canada's Eugenie Bouchard and into the Australian Open third round Thursday as her quest for a record-equalling 24th Grand Slam title gathered pace.

The American won 6-2, 6-2 in 70 minutes, setting up unseeded Ukrainian teenager Dayana Yastremska as the next hurdle in her bid for another major to equal the mark set by Australian great Margaret Court.

The 37-year-old won her 23rd major Down Under two years ago while two months pregnant and is the bookies' favourite to claim an eighth Australian title, despite being seeded 16th.

Williams said she was wary of Bouchard, who is on the comeback trail after a slide down the rankings to number 79 in the world.

"It wasn't an easy match tonight, Eugenie's been to the final of Wimbledon (in 2014) and the semi-finals of other Grand Slams," she said.

World number one Simona Halep limped into an Australian Open third round clash with Venus Williams Thursday after being pushed to the limit by unseeded Sofia Kenin over three sets.

The Romanian downed the 37th ranked American 6-3, 6-7 (5/7), 6-4 over two-and-a-half hours in another unconvincing display after also struggling in her opening match.

The pressure on the reigning French Open champion will only intensify in her next round, when she faces seven-time Grand Slam champion Williams.

"I have no idea how I won this tonight, it's so tough to explain what happened on court," a drained-looking Halep said after overcoming the dogged Kenin, who is fresh from winning the warm-up Hobart International.

Sixth seed Elina Svitolina said she was growing in confidence after a straight sets romp into the Australian Open third round on Thursday.

The Ukrainian, who scored her biggest career win by clinching the WTA Finals in Singapore last October, dismantled Viktoria Kuzmova of Slovakia 6-4, 6-1 in 67 minutes.

"I was trying to be light on my feet and be really quick and I think this was the key today," she said.

Seven-time Grand Slam champion Venus Williams made a late charge into the Australian Open third round Thursday, grinding out a win in her second three-set victory of the tournament.

The unseeded 38-year-old American came back strongly to beat Alize Cornet of France 6-3, 4-6, 6-0, setting up a meeting with top seed Simona Halep.

Williams, who played her first Australian Open in 1998, said she drew energy from the Melbourne Park crowd in the deciding set against world number 36 Cornet.

World number one Novak Djokovic said he could feel the tension before overcoming his great rival Jo-Wilfried Tsonga 6-3, 7-5, 6-4 at the Australian Open on Thursday in a repeat of their 2008 Melbourne final.

The top seed vanquished the Frenchman, who he described as "one of my greatest rivals", for the 17th time in 23 tour meetings stretching back 11 years and advances to face Canada's 25th seed Denis Shapovalov in the third round.

Djokovic, 31, won the first of his 14 Grand Slams in that final against Tsonga over a decade ago and he said the memories came flooding back as the pair walked back out on Rod Laver Arena.

"You could feel the tension on court at the beginning. We felt a lot of emotion," said Djokovic as both players took a trip down memory lane.

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