MELBOURNE, Australia (AP):

SERENA WILLIAMS was having what she called an "out-of-body experience" yesterday in brutal heat at the Australian Open.

Closing the Rod Laver Arena roof and cranking up the air conditioning helped the 2007 champion pull herself together and advance to the semi-finals - but left her opponent steaming.

"I felt I was watching someone play in a blue dress, and it wasn't me, because it was so hot out there," said the second-ranked American, who beat Russia's Svetlana Kuznetsova 5-7, 7-5, 6-1. "And I kept trying to tell myself that it's not hot. But it got hotter."

Williams, seeking her fourth Australian title and 10th Grand Slam championship overall, next faces Olympic gold medallist Elena Dementieva, who had to play her entire match with the roof open. The fourth-seeded Dementieva ousted Carla Suarez Navarro 6-2, 6-2 to run her winning streak to 15 matches after she won two tune-up tournaments.

Top-ranked Rafael Nadal won his fifth match without dropping a set, by beating Gilles Simon 6-2, 7-5, 7-5, though he was strongly tested by the sixth-seeded Frenchman. Simon broke his serve three times - matching Nadal's total for the tournament - and had a set point with the Spaniard serving at 4-5 in the second set.

Quickest players

Nadal was up to the task, ripping several winners on the dead run that were never inside the court until they landed and skipped away untouched.

Simon won their last meeting in Madrid in October.

"I was coming to the match with some doubts," Nadal said. "But I knew I was playing better here."

Simon is one of the quickest players around, but Nadal just ground him down by constantly sending him sprinting from corner to corner. Even with the roof still closed, the lanky Frenchman was pouring out sweat.

Nadal got his seventh service break on a forehand that caught the line for a 6-5 edge in the third set, then held at love with Simon sending a forehand long on match point.

His victory set up an all-Spanish semi-final, with 14th-seeded Fernando Verdasco - the lowest-ranked player to reach the quarter-finals - earlier beating No. 5 Jo-Wilfried Tsonga, last year's runner-up, 7-6 (2), 3-6, 6-3, 6-2.

"I think it's incredible for us," Nadal said. "One will be in the finals, so we have to be happy with that."

The heatwave was forecast to continue yesterday. If Williams wins - Dementieva has won their past three meetings, including the Olympic quarter-finals - she would play a Russian for the third consecutive match in the final. Third-seeded Dinara Safina is facing fellow Russian Vera Zvonareva in the other semi-final.

"Me against the Russians, I guess," Williams said.

With temperatures soaring to 43C (109F) on a cloudless day - moths were dying within seconds of touching down on the blistering surface and Williams had her racquets restrung during her match because they lost their tension - the retractable roof was closed after Kuznetsova won the first set.

Powerful serve

The heat was beginning to take a toll on Williams, and the eighth-seeded Kuznetsova was angry at the decision. She felt that the break gave Williams time to recover and that playing indoors benefited the American's powerful serve.

"Why should I not be?" Kuznetsova said. "Game going my way. I was very comfortable playing outside. It's two different games. One you play inside; one you play outside. Serena was tough. She's playing great. I give her credit. But I don't get this rule."

Neither did other players.

Even though Dementieva won, she felt the roof should have been closed before her match started. Tournament officials called a news conference to explain the decision-making process, bringing in the official doctor and meteorologist to talk about the 'Wet Bulb Globe measure' that determines when it's too hot.

"We do this to protect the players and to protect their ability to perform optimally," said tournament director Craig Tiley.