The world No.1, who claimed the title in 2004 but missed last year's Australian Open, breezed past the first set but was broken by the world No.73 at the beginning of the second set and trailed at 2-0.

Henin refused to give Aiko any more chance and fought back to win her second meeting with the 24-year-old Japanese.

Defending champion Serena Williams also cruised into the second round after a 6-3, 6-3 win over wildcard Jarmila Gajdosova.

The seventh seeded Williams totally dashed the hopes of the home player by her powerful serves and returns.

Russian Maria Sharapova managed a 6-4, 6-3 win over Jelena Kostanic Tosic later on Monday.

Sharapova, who entered the final of the tournament last year but was defeated by unseeded Serena Williams, will face a test against Lindsay Davenport in the next round.

"It's going to be a completely different opponent than the opponent I played today. Lindsay is a big hitter, has a big serve. She is more of a 1-2 ball combination type of player. It's going to be very important to serve well and return well and hopefully get a good hit on the first ball," said Sharapove.

In the men's first round, ninth seed Andy Murray had his Australian Open dream ended by Wilfried Tsonga, as Murray lost the match 5-7, 4-6, 6-0 and 6-7 and became the only top 10 seed that lost on Monday.

Elsewhere, second seed Rafael Nadal survived a two and a half hours marathon against Viktor Troicki 7-6, 7-5 and 6-1 to enter the second round, while sixth seed Andy Roddick won out in straight sets against Lukas Dlouhy of the Czech Republic.

Spaniard Tommy Robredo, No. 11 this year, had a scare against Mischa Zverev but won out eventually after a marathon five-setter.