MELBOURNE (Reuters) - Sloane Stephens bolstered her claim as an eventual successor to Serena Williams by battling through to the Australian Open quarter-finals on Monday, as defending champion Victoria Azarenka advanced with a ruthless return to form.

Sloane Stephens of the U.S. hits a return to Bojana Jovanovski of Serbia during their women's singles match at the Australian Open tennis tournament in Melbourne January 21, 2013. REUTERS/Damir Sagolj

The Gallic juggernaut rolled on at Melbourne Park with Jeremy Chardy's fairytale run continuing and Jo-Wilfried Tsonga overhauling compatriot Richard Gasquet to ensure at least two Frenchmen in the last eight.

It was 19-year-old American Stephens, however, who enjoyed her place in the afternoon sun, reaching her maiden grand slam quarter-final with a hard fought 6-1 3-6 7-5 win over Serbia's Bojana Jovanovski at Hisense Arena.

Both struggled with their serve in a tense final set, but the 29th-seeded American stood firm when it mattered most to secure a A$250,000 (165,513 pounds) payday when her shrieking opponent doffed a return into the net.

"I'm sure my mum's had, like, four heart attacks," Stephens said courtside, raising a laugh from the crowd.

"I try to save all my money because I don't want to be old and broke. I'm still trying to save my money but I'll definitely buy something nice."

Stephens, whose previous best at the majors was a fourth round exit at Roland Garros, will next face fellow American Williams or 14th seeded Russian Maria Kirilenko, who play in the evening session at Rod Laver Arena.

Williams can make it two Americans in the last eight of a grand slam for the first time since the 2010 tournament when she won the title and older sister Venus exited in the quarter-finals.

It was far smoother sailing for world number one Azarenka, who was back at her ruthless best in a 6-1 6-1 demolition of 47th-ranked Russian Elena Vesnina.

Azarenka was the first player in the women's top four seeds to drop a set when she was taken the distance in her previous match by American Jamie Hampton.

The tall Belarusian set herself the goal of improving "everything" after that match but hardly needed to worry against Vesnina, who crumbled to defeat in less than an hour.

With Williams having made the fourth round, Azarenka's number one ranking remains on a knife-edge and only a successful title defence will allow her to keep it.

CONFIDENT CHARDY

She faces a stiffer challenge in the quarter-finals against another Russian in Svetlana Kuznetsova, who sent 10th seed Caroline Wozniacki spinning out of the tournament and out of the top 10, when the next round of rankings are released.

The march of the French has seen tri-colour flags waving at Melbourne Park, where four of the country's men made the last 16 for the first time since 1998.

Chardy ensured more cheer for France, as he overcame a sluggish start to topple Italy's Andreas Seppi 5-7 6-3 6-2 6-2 to secure his maiden grand slam quarter-final.

Unfancied and unseeded, the scruffy-bearded Chardy, ranked 36th in the world, stunned sixth seed Juan Martin del Potro in his previous match and will face the winner of Andy Murray and another Frenchman in Gilles Simon.

"(It's) just like a dream," the thrilled 25-year-old told reporters.

"I know I can beat everybody. So when I feel confident, I believe in me. Against Del Potro, I played a very good match. So it was good for my head."

With seventh seed Tsonga advancing after edging ninth seed Gasquet, France have reached their record of two men in the quarter-finals at Melbourne Park, last achieved in 2009.

The 14th seed Simon has a chance to become a third with a win over Murray, but all but wrote himself off after a five-set marathon against compatriot Gael Monfils which ended early on Sunday morning.

Kuznetosova, the 2004 U.S. Open champion and winner at Roland Garros in 2009, continued to fly beneath the radar with an absorbing 6-2 2-6 7-5 victory over Wozniacki.

Having spent much of last year on crutches with a knee injury, the 27-year-old Russian was thrilled to secure her third quarter-final at Melbourne Park.

"If you had asked me before coming to Australia I would have laughed, definitely," said Kuznetsova of her surprising run.

Roger Federer will bid to advance to a 35th consecutive quarter final when he plays big-serving Canadian Milos Raonic in the late match at Rod Laver Arena.

($1 = 0.9497 Australian dollars)

(Additional reporting by Greg Stutchbury, Nick Mulvenney and Simon Cambers; Editing by John O'Brien)

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