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The defending champion, only seeded 13th this year after injury problems during 2005, served for the match in the 10th game of the second set.

But she failed to hold her serve and was overwhelmed in the tie-break before hitting back for a hard-earned victory.

"I choked today and I didn't do what I needed to do," she said.

Venus slumps to shock exit

"I just lost it basically and I just got really angry that I had put myself in that situation.�There's definitely a lot of things I'm going to work on."

Maria Sharapova put a long-standing injury problem behind her as she powered into the second round of the Australian Open on Monday.

The Russian has been struggling with a rib injury since last summer but was too strong for German Sandra Kloesel.

Sharapova dominated from the outset and wrapped up a 6-2 6-1 victory in exactly one hour, sending a strong message to the other leading women.

Her next opponent will be American Ashley Harkleroad, who beat Shuai Peng.

Top seed Lindsay Davenport made swift progress in the day's opening match without being at her best.

I was excited to get out there and play Lindsay Davenport

The world number one saw off Australian wild card Casey Dellacqua 6-2 6-1 in the opening match on Rod Laver Arena as temperatures soared in Melbourne.

A sluggish start saw both players struggle on serve but world number 180 Dellacqua made more unforced errors.

Venus out, Dementieva out, Moya out. You see, there is just no such thing as an easy draw From Aussie Manics Have your say on Five Live

Davenport's class proved too much and the American goes on to face Alona Bondarenko or Karolina Sprem.

"I was actually a little nervous," said Davenport.

"I don't know if that's just because I've been counting the days down the last few days because I wanted to play.

"I was excited to get out there and play. I was jumping around, ready to go."

Justine Henin-Hardenne sent out a message to her Australian Open rivals with an impressive 6-2 6-1 first round win over Marta Somachowska.

The 2004 champion, who won last week's Sydney International, needed just over an hour to wrap up victory.

"I've been a little bit surprised with the quality of my game last week," she said. "For my first tournament back I wasn't sure I could play this tennis."

Meanwhile 14th seed Svetlana Kuznetsova eased past Lauren Breadmore 6-1 6-3.

Jelena Dokic admitted she "couldn't focus mentally" after what she thought was a match-winning forehand was called out by the umpire.

Making her return to the Australian Open after four years away, she went on to lose to 3-6 7-6 (8-6) 6-1 Viirginie Razzano.

Slovakia's Daniela Hantuchova, the 17th seed, fought back for a 3-6 6-3 6-0 win over Japan's Saori Obata, but 24th seed Tatiana Golovin of France went down 6-4 4-6 6-4 to Italy's Mara Santangelo.