Defending Australian Open champion Serena Williams came dangerously close to booking her ticket home alongside sister Venus.

In her 27th grand slam tournament, Williams at one stage looked like she might fall in the first round for the first time, before triumphing 6-3 6-7 (1-7) 6-2 against China's Li Na.

It was her 15th consecutive win at Melbourne Park, having won the 2003 and 2005 Opens, missing the 2004 tournament through injury.

She had earlier jokingly told Venus, who was a shock 2-6 6-0 9-7 loser to Bulgarian Tszvetana Pironkova, that she wished she could join her on the trip back to the United States.

"I told her I was a bit envious that she gets to go home, so she could cheer up," Serena said.

"By no means am I envious but I was just trying to get her to cheer up, that's all."

She looked like she might be taking her words of consolation too seriously at one point when she frittered away a chance to close out the match while serving at 5-4 up in the second set.

Williams threw up consecutive double faults to lose that service game, then in the subsequent tiebreak was steamrolled by Li, to take it into a third.

Li broke serve in the opening game of the final set and with the momentum going her way, a second major upset of the opening day looked on the cards.

Williams admitted she had choked slightly while trying to serve out the match.

"I just lost it basically, I don't know, I didn't do what I needed to do and Li played some great shots, she started hitting winners from the back court and I don't know what I did," she said.

But she said that experience caused her to stop playing cautious tennis and start going for winners, a change of outlook that helped her storm home in the final set and which she would carry into the second round.

The tight match, which took more than two hours, at least gave her the opportunity to answer the questions about her fitness that had dogged her in the tournament lead-up.

"I feel amazing right now, I just feel like dancing ... I have a lot of energy right now," she said.

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