MELBOURNE, Australia (AP):

VENUS WILLIAMS squandered a match point before losing 2-6, 6-3, 7-5 to 46th-ranked Carla Suarez Navarro in the biggest upset so far at the Australian Open.

Williams hardly looked like the reigning Wimbledon champion against the 20-year-old Spaniard, who reached the French Open quarter-finals last year as a qualifier in her first Grand Slam.

Usually the aggressor with her powerful shots, sixth-seeded Williams was sluggish yesterday as she was broken while serving for the match and dropped the last five games with the crowd cheering loudly for Suarez Navarro to finish off the victory.

Super consistent

"She was super consistent and aggressive and just went for her shots," said Williams, who has seven Grand Slam titles and now can only hope for a doubles crown here with sister Serena. "Probably one of her best matches she's ever played. "I wasn't in control of the points. I'm definitely used to dictating the points a little bit more. It was kind of a pattern that wasn't the best for me."

Serena Williams struggled earlier and headed to the practice courts after a 6-3, 7-5 win over Argentina's Gisela Dulko, ranked 45th. Williams gave her performance a "D-minus at best".

Rafael Nadal got high marks for a 6-2, 6-3, 6-2 win over Croatia's Roko Karanusic.

His potential semi-final rival, fourth-ranked Andy Murray, wasn't seriously challenged in his first real test, ousting 51st-ranked Marcel Granollers of Spain 6-4, 6-2, 6-2 in one hour and 50 minutes.

The top-ranked Nadal has dropped only 11 games in six sets and next faces Germany's Tommy Haas, who beat Flavio Cipolla of Italy.

Nadal's biggest problem was finding a rhythm against the inconsistent, 92nd-ranked Karanusic, who has never made it past the second round in 11 Grand Slams.

Rigorous training

Murray only had to be on court only 45 minutes in Tuesday's stifling heat before Andrei Pavel retired with a back injury. With Scottish flags and tartan hats scattered around Rod Laver Arena on a cool evening, Murray had 37 winners to 18 for Granollers. He credited a rigorous offseason training programme.

"As a result, I got a little bit more power on my serve," said Murray, runner-up at the US Open last year. "All the work I did is paying off. This is probably the best I've felt coming into a Grand Slam."

Suarez Navarro, overmatched at first, broke twice in the second set as the 28-year-old Williams let a number of reachable shots fly past. She saved a match point while serving at 4-5 in the deciding set and broke in the next game, aided by a Williams double-fault.

Williams netted a forehand on match point in the next game for her 37th enforced error.

Suarez Navarro said she had little choice but to go for her shots.

"You must be aggressive during all the match because, if not, she's going to take control of you."

Serena Williams said her victory left "lots and lots and lots of room for improvement" but she was happy to get through without her best form.

She looked to be headed to a quick victory - by the time Dulko hit her first winner, she already was down 3-0. But the Argentine soon was matching the powerful Williams shot for shot. She saved triple set point while serving at 2-5, but Williams finished it off the next game with a pair of aces.

In the second set, Dulko - who said she wasn't sure she'd be able to play after running a high fever following a doubles match the day before - served at 5-3 in and held six set points in a game that went to deuce 12 times. But Williams hasn't won nine Grand Slams by caving in to pressure and finally converted breakpoint number seven.

"It was a very tough second set; she started playing unbelievable, hitting winners left and right," Williams said. "She had a couple of opportunities, but I always felt I wasn't going to lose."

Improved chances

Olympic champion Elena Dementieva improved her 2009 winning streak to 12 matches by beating Iveta Benesova. The 27-year-old Dementieva reached the French Open and US Open finals in 2004 but has not returned to the final of a major since.

Amelie Mauresmo, who won here and at Wimbledon in 2006, rallied to beat Britain's Elena Baltacha while fellow Frenchwoman Virginie Razzano ousted number 14 Patty Schnyder of Switzerland 6-3, 6-1.

Other women advancing included number eight Svetlana Kuznetsova of Russia, number. 12 Flavia Pennetta of Italy, number 13 Victoria Azarenka of Belarus, number 18 Dominika Cibulkova of Slovakia, number 21 Anabel Medina Garri-gues of Spain and number 22 Zheng Jie of China.

On the men's side, number nine James Blake won in straight sets for the second time, never dropping serve while beating Sebastien de Chaunac.