World number five Maria Sharapova ground her way into an eighth Australian Open quarter-final Sunday, downing highly-rated Swiss teen Belinda Bencic after a titanic struggle.

The Russian five-time Grand Slam champion needed two hours, five minutes to get past the 12th seed 7-5, 7-5 on Rod Laver Arena and set up a potential last-eight clash with arch-rival Serena Williams.

The world number one is on court later Sunday against Russian Margarita Gasparyan with a victory pitting her against Sharapova, whom she beat in last year's final. She has won all their contests since 2004.

"These are the players that will ultimately take our spot," she said of the talented Bencic. "But not just yet."

"I was really focused today," she added. "It's always great to play against the players coming up for the first time."

Bencic, the WTA's highest ranked teenager, has gone from rising star to the real deal over the past year, having already claimed 10 top-10 wins in her career.

Coached by Melanie Molitor, mother of Martina Hingis, she won tournaments in Eastbourne and Toronto in a breakout 2015 and was a major hurdle for the Russian.

But Sharapova -- the last teen to win a Grand Slam title, aged 19 at the 2006 US Open -- has been in good touch at Melbourne Park, where she won in 2008, and ultimately her big-match experience proved decisive.

- Ends on a challenge -

She easily held for 1-0 then applied pressure to the Bencic serve with some pinpoint groundstrokes.

The teenager held on to keep it at level-pegging but the Russian kept pressing and had two break points in the fourth game, with the Swiss keeping her cool to stay in the set.

Sharapova is well known for her solid backhand, but it has the forehand she has been relying on in Melbourne so far, and she put it to good effect again, drilling winners.

But her serve can run hot and cold and a double fault gave Bencic her first break point, and a backhand into the net gifted the young gun a 4-3 lead.

Sharapova wasted no time in breaking straight back but her hit-and-miss serve again let her down and Bencic reclaimed the advantage with a sizzling backhand down the line.

Neither player could hold serve and the Russian was soon back at 4-4 on her third break point of the game when Bencic snatched a backhand wide.

Sharapova finally held serve and, shouting "C'mon!", carved out two set points in the 10th game -- but failed to convert either.

It was a huge battle with little between them. The Russian hung on to take a 6-5 lead and finally won the set after 64 minutes when Bencic scooped a backhand wide.

The first game of the second set lasted 11 minutes, as the struggle for dominance continued.

It went with serve till 2-2 as they battled to gain the upper hand. Bencic had her first break point but a clinical Sharapova stayed in control and had a break point herself on the Swiss star's next serve only to be denied.

Neither could find an opening until the 12th game when Sharapova screamed in joy after winning a challenge on a deep baseline shot that handed her victory on her second match point.