Sixth seed Venus Williams crashed out of the Australian Open in the second round on Thursday, extending her jinx at the season-opening Grand Slam with a shock loss to Spain's Carla Suarez Navarro.

The seven-time Grand Slam champion went down 2-6, 6-3, 7-5 to world number 46 Suarez Navarro, ending her dream of claiming one of the few goals in the tennis world to elude her.

Williams was on a 10-match winning streak and regarded as one of the form players at the Australian Open, a tournament she has now failed to win in 10 attempts.

She looked in control early in the match but could not wear down the 20-year-old Suarez Navarro in a two hour 14 minute marathon squandering match point in the third set.

Williams, 28, who fell at the first round here in 2006, said she still felt such losses as keenly as when she began her career.

"I don't like to lose just as much as the first day when I started playing, so it's still the same," she said. "I mean, losing's never the best fun, to say the least, but fortunately I've also had a lot of nice wins, too, so hopefully that will balance it out."

It is only the fifth time the American has been dumped out of a Grand Slam before the third round in her illustrious career and her earliest exit at a Major since 2006.

Williams praised her opponent, who was a surprise quarter-finalist at last year's French Open.

"She was super consistent and aggressive and just went for her shots," the reigning Wimbledon champion said. "I think she just played really well."

Williams said she would have to overcome her disappointment to play a doubles match with sister Serena on Friday and would then analyse what went wrong.

Suarez Navarro was at a loss to explain the upset. "I don't know, I only play, I don't know what to say," she said before a roaring crowd at the Rod Laver Arena.

Crucial game

Williams broke Suarez Navarro in the opening game, using a height advantage of almost 25 centimetres (10 inches) to attack the net.

She also overpowered the Spaniard with her serve, with Suarez Navarro showing early signs of nerves and going down another break in the fifth game.

A rout looked on the cards as Williams served out the first set after 29 minutes but Suarez Navarro settled in the second set, snatching a break and racing to a 3-0 lead.

The American lifted her intensity and broke back in the seventh but Suarez Navarro refused to wilt, successfully drawing Williams into a baseline slugfest to regain the advantage in the next game.

She was rewarded with three set points, Williams hitting a forehand long in the third to give Suarez Navarro the set after 42 minutes. The Spaniard went toe-to-toe with Williams early in the third, fending off a break point for the American in the second game.

Williams finally achieved a break in the fourth as Suarez Navarro double faulted in windy conditions, only to come within a point of surrendering the advantage in the next.

She held on with an ace to go 3-1 up but struggled to maintain control of the match and Suarez Navarro broke back in the ninth to make it 5-4.

Williams reached match point with the Spaniard serving in the next but hit her return long and her opponent evened the score at 5-5. Suarez Navarro turned the tables to earn two match points at 6-5, netting the first but winning after Williams' return went long.