The fallibility of the latest tennis technology was exposed at Melbourne Park when a ball that appeared to be out on replays was ruled in by the controversial "Hawk Eye" line calling system.

The embarrassing situation arose when defending champion Amelie Mauresmo challenged a call on set point in the opening set, claiming a ball called in on the baseline was, in fact, out.

The courtside screens showed the ball touching down over the line, but amazingly declared it "in".

A magnified image shown to courtside patrons revealed a fine margin between the ball and the baseline, prompting Mauresmo to point to the screen and again call on the umpire to overturn the call.

Fortunately, the incident ended up having little impact on the match with Mauresmo winning the next point and wrapping up the set.

The world No.3 went on to take the match 6-2 6-2.

Apart from some notable exceptions, players have generally welcomed the new system of challenging calls which are then viewed by an official watching the "Hawk Eye" simulation that has been a part of televised cricket coverage for several years.

But men's No.1 Roger Federer regards the system as "nonsense" saying they encouraged umpires to avoid making a call.

"Now they (umpires) can hide behind these calls," Federer said.

"They tend to now just let us do the work, you know, the tough stuff."

Earlier on Wednesday, a rusty, daydreaming Serena Williams continued her comeback, rolling into the third round with her 7-6 (7-4) 6-2 defeat of Anne Kremer of Luxembourg .

The win set up a far more testing match up against fifth seed Nadia Petrova.

Williams, a seven-time grand slam winner and dual Australian Open champion, spent most of last year recovering from a knee injury, her absence causing her ranking to slide to its lowest ever point.

While she is aware she might never make it to the top of the pile as she did as a 20-year-old, Williams, who is now ranked 81st, is looking forward to getting through another couple of rounds in Melbourne.

Petrova, though, will be a far more serious opponent than the two she has beaten so far.

"It's definitely a step up, I feel excited to go into the match, I feel ready," Williams said.

But she may need more than excitement and a sense of readiness to get past Petrova.

"I'm still working on some things ... I need to stay more focused," she said.

"I think I lost a little focus like when I was up 4-0 in the second.

"I started daydreaming. I'm too experienced to daydream at that stage of a match."

Petrova made even easier progress into the third round, knocking out Argentina's Gisela Dulko 6-1 6-2.

For the Russian, victory over Williams would be revenge for her fourth round loss to her in 2005 when the American went on to win the championship.

Since then Petrova has improved her ranking from 12th to sixth but has failed to get past the quarter finals of a grand slam event on any surface other than clay.

In other second round matches Russian players were to the fore all around Melbourne Park.

Ninth seed Dinara Safina had the better of fellow Russian Ekaterina Bychkova 7-6 (7-5) 6-1; Vera Zvonereva (22) beat Israel's Tzipora Obziler 6-3 6-4; Elena Dementieva (7) beat Martina Muller of Germany 7-5 3-6 6-0 and Svetlana Kuznetsova (3) beat Australia's Monique Adamczak 6-2 6-1.

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