Dangerous floater Victoria Azarenka and Caroline Wozniacki will put their long-time friendship on hold when they square off in a mouth-watering Australian Open second-round match between two former world number ones.

Azarenka began her campaign for a third Open title on Tuesday with a 6-3 6-2 victory in the grudge match against Sloane Stephens, her third straight-sets win over the American at Melbourne Park in as many years.

Both players were unseeded – with Azarenka having battled foot and knee injuries and personal issues in 2014, while Stephens suffered a slump in form.

In Stephens’ first match against Azarenka two years ago, the American accused the Belarusian of gamesmanship for taking a long medical timeout midway through their semi-final.

Last year, Stephens hit a forehand into Azarenka’s groin region during their fourth-round match, with the American’s attempts to apologise being ignored by the 2012 and 2013 Australian Open champion.

There were no further flashpoints on Tuesday, with Azarenka – who shapes as the most problematic spoiler in the draw – advancing to a second-round clash on Thursday against Wozniacki, the No.8 seed and 2014 US Open finalist.

“That’s going to be a tough match for me, being an unseeded player,” said Azarenka.

“It’s not a surprise that I have a tough draw or tough opponents in the early rounds.

“I just need to go through that and I accept the challenges.

“She was showing some great tennis in the end of last year and I know she’s very dangerous.”

Wozniacki was made to work hard in the first set by American Taylor Townsend before lifting in the second to win 7-6 (7-1) 6-2.

Like Azarenka, the Danish star endured a rocky 2014 off the court, splitting with her fiance, golf superstar Rory McIlroy.

She holds a 5-3 advantage in her head-to-head career record against Azarenka.

“We’ve known each other for over 10 years and we’ve competed for a very long time so we go way back,” said Wozniacki.

“We’ve always been pretty close.

“She’s a fun girl to be around and there’s always loads to talk about.

“I’m glad to see her back.”

After being bounced out in the first round at Melbourne Park last year by unheralded Thai Luksika Kumkhum, two-time Wimbledon champion Petra Kvitova was nervous heading into her opening clash with Dutch qualifier Richel Hogenkamp.

But the fourth-seeded Czech proved too strong, winning 6-1 6-4.

“I’m happy to have won,” said Kvitova.

“I’ve never played her before and never seen her play so that’s always difficult.”

Last year’s Open runner-up Dominika Cibulkova overcame a first-set blip to beat Belgian Kirsten Flipkens 3-6 6-3 6-1.

The Slovakian is seeded 11th, having enjoyed her best year on the tour in 2014.

Australian standard-bearer Samantha Stosur, the No.20 seed, crushed Romania’s Monica Niculescu 6-4 6-1.

No.19 seed Alize Cornet from France beat China’s Zhang Shuai 6-3 6-2 and No.24 Garbine Muguruza from Spain ousted New Zealander Marina Erakovic 7-5 6-0.

Germany’s Andrea Petkovic was a rare seeded casualty on Tuesday with the No.13 falling 5-7 7-6 (7-4) 6-3 to American Madison Brengle.