By Nick Mulvenney

MELBOURNE (Reuters) - Rafa Nadal really hit his stride to reach his fifth straight quarter-final at the Australian Open and will be keen to keep the momentum going against fellow Spaniard David Ferrer on Wednesday.

"We know each other perfectly, we played a lot of times against each other," said the 24-year-old, who holds an 11-3 record against Ferrer but lost their last grand slam clash at the 2007 U.S. Open. "I think he's a fantastic player to spend so many years in the top positions.

"That's very difficult to do. So all respect to him. I know it's gonna be a really, really difficult match."

Victory in the evening match on Rod Laver Arena would set up a semi-final with British fifth seed Andy Murray or surprise package Ukrainian Alexandr Dolgopolov, who play earlier.

Murray, last year's losing finalist, is the meanest player still in the tournament having conceded just 21 games in four matches and not spent more than two hours on court in any of his encounters.

The 23-year-old Scot has been in intimidating form but will be well aware that the Melbourne Park debutant Dolgopolov's fierce groundstrokes and "funky" style did for fourth seed Robin Soderling in the fourth round.

Like Murray, Vera Zvonareva has played two grand slam finals and ended up a loser both times but the Russian believes she may now have the maturity to claim her maiden major.

The women's second seed opens day nine of the Australian Open with her quarter-final against dangerous Czech left-hander Petra Kvitova, who upset local hope Sam Stosur in round three.

Kim Clijsters will be a strong favorite to beat Poland's Agnieszka Radwanska in the other quarter-final and move into a sixth semi-final at the year's opening grand slam.

Radwanska, 21, is playing her first tournament since October after having surgery on a stress fracture in her foot and promised to play with freedom against the three-times U.S. Open champion.

"I think now there is no pressure," she said. "I just feel very good after my very short off-season. She's a great champion, so I have nothing to lose. So I'm just going to try and play my best tennis and try to win.

(Editing by Martyn Herman)