Updated

By Greg Stutchbury

MELBOURNE (Reuters) - Forward. Left. Backward. Right. Attack. Jump. Run. Defend. Counter-punch. Run. Celebrate. Shake hands. Talk to media. Eat. Sleep. Start again.

Such is the rhythm needed for a successful tennis player at the Australian Open and Justine Henin believes, despite the fact she advanced to the semi-finals at Melbourne Park on Tuesday after she beat Nadia Petrova, she is still struggling to find it.

"It was difficult to play (a) night match two days ago and be first at 1100 (on Tuesday)," she told reporters after her 7-6 7-5 victory over the 19th seeded Petrova on Rod Laver Arena.

"It's been kind of strange as I had to get used to another rhythm," she added of moving from night to day matches.

It is no surprise Henin is still struggling with the tournament's vagaries, complaining of fatigue and finding it difficult to recover.

The seven-times grand slam winner is playing only her second tournament back after returning from an 18-month retirement and her run is beginning to draw parallels with that of compatriot Kim Clijsters' at the U.S. Open last year.

The victory for Clijsters was in just her third tournament back, following her own two-year layoff, though Henin said that had not given her any additional confidence she could return to the game at the highest level.

DIG DEEP

"I mean, what she did, I did admire that a lot because it's not easy what she did in New York," Henin said. "If I see it as motivation, of course. That means it is possible.

"But we have very different kind of personalities, different kind of players, so it's always very hard to compare. That will be a dream for me to do it also."

Henin has had to dig deep to make the semi-finals. She beat fifth seed Elena Dementieva in the second round, world number 16 Yanina Wickmayer in the fourth and faced a tough opponent on Tuesday against Petrova.

The Russian, who had lost to Henin in the first round in Brisbane, had already knocked out Clijsters and French Open champion Svetlana Kuznetsova on her way to the quarter-finals.

Henin won the tight first set in a tie-break and then had to claw her way back from a 0-3 deficit in the second before she sealed her semi-final against China's Zheng Jie.

"I felt energy in a few games, and then the intensity, I lost it a little bit, especially in the beginning of the second set," Henin said.

"When I had to play well in the tiebreak, and at five all in the second, that's what I did.

"So I keep going. I'm happy. It's just a great feeling to be in the semis of the first grand slam I play since I'm back."

(Editing by John O'Brien)