Melbourne: Defending champions Roger Federer and Amelie Mauresmo overcameearly jitters to negotiate the first round of the Australian Open Monday on aday overshadowed by brawling Serbian and Croatian fans. 

 Unseeded seven-time Grand Slamchampion Serena Williams breezed through her match against Italian 27th seedMara Santangelo 6-2, 6-1, dispelling doubts about her fitness after an aninjury-plagued 2006.

But fourth seed Ivan Ljubicic crashed out, unable to get to grips withAmerican Mardy Fish, losing 4-6, 7-6 (7/2), 6-4, 6-4 to become the highestprofile casualty on day one.

Russia's Marat Safin, the 2005 champion and twice runner-up, teetered on theedge of elimination before winning a five-set thriller against German BenjaminBecker 5-7, 7-6 (7/2), 3-6, 6-3, 6-4 in 3hr 26min.

While the tennis went mostly to form, age-old ethnic rivalries betweenSerbian and Croat fans boiled over.

Wearing the national colours of the bitter Balkan rivals, the two sidesclashed after taunting and hurling insults at each other.

Dozens of police were called in and ejected around 150 of them afterconfiscating their tickets.

"They were mostly Serbians ejected as they were upsetting the Croatians,"Victoria Police spokeswoman Katherine Jess said.

Tennis Australia chief executive Steve Wood said there were no injuries orarrests and praised security staff for acting swiftly to end the trouble.

Unaware of the commotion, the Fed Express, bidding for his third AustralianOpen title and 10th Grand Slam, stuttered through his first set against GermanBjorn Phau before finding his groove to post a 7-5, 6-0, 6-4 win.

It sets up a second clash with veteran Swede Jonas Bjorkman.

Under cloudy skies and with a smoke haze from bushfires in the air, theSwiss world number one admitted he had to battle hard before getting the upperhand.

"I'm happy to be through because it looked like I was definitely goingto head for a first set loss," he said.

"But I came through, that's the most important thing," he said.

Andy Roddick, who beat Federer in the exhibition Kooyong Classic final onSaturday, was also given a fright, losing the first set after a mammothtiebreak to French wildcard Jo-Wilfried Tsonga before going 2-5 down in thesecond.

The American pulled himself together and rallied to a 6-7 (18/20), 7-6 (7/2)6-3, 6-3 victory and will now play another Frenchman Marc Gicquel.

Others through included ninth seed Mario Ancic of Croatia,the evergreen Dominik Hrbaty of Slovakia,seeded 22, and former French Open champion Juan Carlos Ferrero, seeded 24.

Last year's finalist Marcos Baghdatis of Cyprusscratched his way to a 6-4, 2-6, 6-3, 6-2 win over Germany's Rainer Schuettler, andsaid it was unsettling being back at the scene of his career tennis highlight.

"It's not like a normal tournament for me, and that's all. It's like adifferent tournament and I'm not used to it. I have to just find my way,"he said.

Mauresmo, the second seed behind Maria Sharapova, fought past Shenay Perry6-3, 6-4.

The Frenchwoman, who also won Wimbledon last year for Grand Slam successafter a decade of frustration, proved too powerful for the American but it wasa decent workout ahead of her next match against Olga Poutchkova of Russia.

"(It's) not yet quite the feeling that I had at the end of thetournament last year but the first match is never easy," said the theGeneva-based 27-year-old, who has shaken off her tag as a choker.

Williams, who won the title here in 2003 and 2005, said she was feelingbetter than she had in a long time and believed she could win a thirdAustralian crown.

"I'm excited to be back out here and I came out and finally did whatI'm supposed to do to a certain level," she said.

Other women through included Russian seventh seed Elena Dementieva, Serbian11th seed Jelena Jankovic and Czech Republic 10th seed Nicole Vaidisova.