MELBOURNE, Australia — Rafael Nadal and Andy Murray held off two of the tallest men and biggest servers in tennis today to set up a quarterfinal meeting at the Australian Open.

Defending champion Nadal had a 6-4, 4-6, 6-4, 6-4 win over 6-foot-10 Ivo Karlovic of Croatia, the tallest man on the tour.

In the previous match at Rod Laver Arena, No. 5 Murray overcame 6-foot-9 American John Isner, 7-6 (4), 6-3, 6-2. Murray hasn't dropped a set in four matches.

Over on Hisense Arena, Nadia Petrova advanced with another upset, beating third-ranked Svetlana Kuznetsova, 6-3, 3-6, 6-1, to reach the quarters.

In the other section of Petrova's half of the draw, Zheng Jie set another national mark by becoming the first Chinese player to reach the quarterfinals at Melbourne Park with a 7-6 (6), 6-4 victory over Alona Bondarenko.

Nadal, who beat Roger Federer in the final here last year to capture his first major on hard courts after four titles at the French and one at Wimbledon, said the strategy against Karlovic was just not to blink.

"Just be focused all the time, move the legs, because you going to have a lot of points only with one shot," said Nadal, who was already looking ahead to a different style of match against Murray.

"Being the quarterfinals is a very good news for me ... I'm going to have a very difficult match against Andy," Nadal said. "It's completely different. He's one of the more talented players on the tour. He can play aggressive, play offensive.

"I want to play my game. ... If not maybe I will have a good flight home."

Murray is into the Australian Open quarterfinals for the first time. He lost the U.S. Open final to Federer in 2008, his only trip to a Grand Slam final, and knows he'll probably have to beat both Nadal and Federer to claim his first major.

The 22-year-old Scot rated Isner's serve among the best in the game, so he was delighted to wear down the American after a crucial service break in the eighth game of the second set. He fended off break-point chances in the next game to serve out the set.

"It's tough. I had my coach serving at me from the service line this morning to try to get used to it," Murray said. "But once you get out there it's kind of tricky."

Murray broke serve again in the seventh game of the third set when Isner netted a forehand and then smashed his racket into the court in disgust.

"It's been good. I moved really well since the start of the tournament," Murray said. "I didn't drop a set yet ... not too much to complain about."

The loss was Isner's first of the year, which started with his first career ATP title at Auckland.

Kuznetsova was only playing her second tournament of the year and was coming off a late finish to her third-round win, wrapping up the match at almost 2 a.m. yesterday after being four points from defeat in a match that started late Friday.

Kuznetsova committed 52 unforced errors compared to 22 winners and had her serve broken three times in the deciding set after rallying in the second to level the all-Russian match.

No. 19 Petrova had a stunning 6-0, 6-1 win over U.S. Open champion Kim Clijsters in the third round. Her run to the quarterfinals equals her best run at the Australian Open. Her best run at a Grand Slam was to the French Open semifinals twice.

"You have to play well if you beat Kim 6-0, 6-1," Kuznetsova said of Petrova. "Sure, Kim was not at her best level to lose like that. It's not only Nadia who played good."

Zheng had already matched her own previous best run at Melbourne Park by reaching the fourth round, but is still a win away from equaling her best performance at a Grand Slam.

The 26-year-old Zheng made a stunning charge to the Wimbledon semifinals in 2008, becoming only the second wild-card entry and first Chinese player to reach the semis at a major.

"I think Australia is lucky for me because I win the first Grand Slam doubles title in Australia," said Zheng, who won the Australian Open and Wimbledon doubles titles in 2006 with Yan Zi. "So I'm so happy I'm in the quarterfinal of Australia also."

She and No. 16 Li Na both reached the fourth round here, the first time two Chinese players have reached that stage at the same Grand Slam tournament. With one on each half of the draw, Zheng said they can both go further.

"But I think we can go the far way," she said. "I hope we can be in the semifinal for both Chinese player, yet."