Updated

By Ian Ransom

MELBOURNE (Reuters) - A shell-shocked Venus Williams struggled to make sense of her stunning quarter-final loss to China's Li Na after blowing a one-set lead and her service game to bow out of the Australian Open Wednesday.

Williams, who has not progressed past the last eight at Melbourne Park since 2003, crumbled when serving for the match at 5-4 in the second set in a 2-6 7-6 7-5 upset.

The sixth seed also failed to capitalize on five service breaks in the decider at Rod Laver Arena.

"I guess the match is so fresh. I can't quite say exactly what happened. I'm still processing it," a downcast Venus told reporters.

"In tennis you have to close it out. It's not like there's a clock ticking and then suddenly it's over. You just have to close it out. I didn't do that today."

Despite making the last eight, Venus's progress in Melbourne had been far from smooth.

Wins over Austria's Sybille Bammer, local hope Casey Dellacqua and Italy's Francesca Schiavone were plagued by poor serving and lapses in concentration.

Against Li, Williams managed to land just 56 percent of her first serves and struggled frequently with her ball toss.

"I think I just started rushing my shots a little too much instead of just taking my time and really just hitting a clean ball," said the American.

"Sometimes I was able to back off. But, you know, sometimes it's so easy to get so eager."

With her 30th birthday approaching, time may be running out for Venus to add to her haul of seven grand slams.

Her last was at Wimbledon in 2008, where she beat younger sister Serena in the final.

She remained defiant, however, and said she would learn from her mistakes and move on.

"Like I said so many times before, if I would have gotten involved in what people said, I would have never left the ghetto," said Venus.

"So here I am playing pro tennis, playing well. The sky's the limit in this sport. I'm looking for that."

(Editing by Alastair Himmer)