World No 91 beats the heat and a Grand Slam legend at Roland Garros

China's Wang Qiang hailed one of the greatest victories of her career after stunning American superstar Venus Williams in the opening round of the French Open on Sunday.

World No 91 Wang's hard-fought 6-4, 7-5 triumph avenged her two previous losses to the seven-time Grand Slam champion.

And Wang reckons the nature of her win over the world No 9 could be something of a watershed for her.

"I'm always too cautious when I play. In other words, I always get cold feet," said the 26-year-old. "For games like this, waiting for opponents' mistakes won't guarantee victory. I had to be more active and aggressive.

"I just wanted to play well and tried to avoid any mistakes. I barely won any games this month. I had to be more decisive. Given her world ranking, I did not have to think too much."

When asked how the win ranked in her career, Wang replied: "At least top three."

The loss marked the first time 2002 runner-up Williams has lost her opening match at Roland Garros since 2001, and the only time in her career she has lost consecutive opening-round matches at a Grand Slam.

"There really are no perfect days in tennis," the 37-year-old mused. "At this point I have just got to look forward. I just want to be my best, that is all. Nobody plans on this."

Venus will now turn her attention to playing the doubles tournament with her sister Serena, who is competing in a Grand Slam for the first time since last year's Australian Open after giving birth to her daughter.

Wang has never made the third round of a Slam, and will face world No 34 Petra Martic of Croatia for a place in the last 32.

The Tianjin native might have been forgiven for rolling her eyes when the draw was made last week, having been beaten by Williams at Roland Garros and at Wimbledon in their only previous meetings.

But Wang set about her task with enthusiasm on sunny Court Suzanne Lenglen, never allowing her rangy opponent to settle into her game.

Compact and busy, Wang looked to be putting more effort into every ball than Williams, who languidly returned long fluid shots.

On a hot day that had both players glistening with sweat by the end of the first game, such differences can count double.

So too can free points and short ones, and both Wang and Williams looked to shorten rallies with heavy groundstrokes aimed at the lines.

When faced with a wingspan like that of Williams, the margin for error is miniscule, and Wang fired shot after shot onto the lines, killing off Williams' scooped, looped backhands with flat varieties of her own.

There was barely a wisp of wind to offer the sweltering players any respite, but Wang, dressed all in black, never took a backward step, sealing the opening set in the 10th game after a flurry of points that kept the frustrated Williams off balance.

The double-fault that Williams hit to lose the first set might have been more indicative of her fortunes, as she struggled to get a good grasp on her game.

She eased her way into a 3-0 lead in the second set, but the smoke and mirrors couldn't mask the holes in her game with Wang taking the ball earlier and striking it with more purpose.

The Chinese was soon level and when Williams double-faulted again - for the fourth time - in the 11th game of the second set, it opened the door for Wang to notch a notable win.

She sealed it, rather fittingly, when Williams clubbed her 35th unforced error into the net.

Beaming with joy, Wang waved to the crowd and skipped up and down as Williams stalked to the locker room.

Williams will expect a better showing at Wimbledon, a tournament she has won five times, but not since 2008. A runners-up finish there last year will also give her cause for optimism.

"I have five weeks, so..." she smiled.

Agencies contributed to this story.