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.

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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.”

Top seed Serena Williams moved one step closer in her pursuit of a 19th grand slam title by crushing Belgian Alison Van Uytvanck 6-0 6-4 on Margaret Court Arena.

Williams began the year with an inconsistent showing at the Hopman Cup, but looked more clinical against world No.106 Van Uytvanck on Tuesday night.

The 33-year-old claimed the first set in 21 minutes before Van Uytvanck found her feet.

Williams looked in a degree of discomfort during the second set after stretching out in a slide, but recovered to close out the match by breaking the Belgian’s serve.

The world No.1 could receive a sterner test in the second round against unseeded Russian Vera Zvonareva, who beat Ons Jabeur from Tunisia 6-2 6-3.

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.”

Polish sixth seed Agnieszka Radwanska thumped Kurumi Nara 6-3 6-0 in a tick over an hour, while 18th seed Venus Williams downed Maria-Teresa Torro-Flor 6-2 6-2.

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 and Italian Flavia Pennetta were the notable seeded casualties on Tuesday.

No.13 Petkovic fell 5-7 7-6 (7-4) 6-3 to American Madison Brengle, with Pennetta going down 4-6 6-2 6-3 to unseeded compatriot Camila Giorgi.

-AAP