Melbourne:Defending champion Novak Djokovic survived a spirited encounter with Bosnian-born American Amer Delic at the Australian Open on Friday before crowd trouble flared outside.
The 21-year-old Serb lost a set for the first time in the tournament and had to fend off two set points in the fourth before beating Delic 6-2, 4-6, 6-3, 7-6 (4).
Moments after Djokovic and Delic had embraced at the net, smiled and waved to all parts of the crowd in Rod Laver Arena, water bottles and plastic chairs were hurled back and forth between the Bosnian and Serb fans who had been watching the match live on a big TV screen next to the arena.
One Bosnian girl was hit in the head and stumbled from the area on the arms of friends as police and security staff rushed to separate the rivals. The loud, angry scuffle was over within two minutes, and police took many of the participants to another area for questioning.
"They started it. They threw the first chair and knocked our girl down and kept throwing things at her," one Bosnian man who would not identify himself said before he was taken away by a police officer.
Victoria state police and organizers had no immediate comment.
There was no animosity on court.
"Of course, I have a big respect for Amer," Djokovic said, to loud cheers from the crowd. "He absolutely deserves your applause and even more. He has one of the biggest serves on tour. It was very difficult for me to read."
No. 127-ranked Delic got into the draw as a lucky loser from qualifying when Nicolas Kiefer withdrew with an injured ankle. Delic rallied to win two five-set matches to make the third round, his best run at a major.
In the tie-breaker, Djokovic challenged a call and stopped a rally, risking losing the point if he was wrong.
He wasn't, forcing a replay and winning the point when Delic double-faulted.
"I might have looked confident, but I was not. It was very lucky," said Djokovic, who beat Roger Federer in the semifinals here last year and claimed his first major. "Sometimes you need luck."
Djokovic next plays the winner of Friday's later match between American Mardy Fish and 2006 runner-up Marcos Baghdatis.
No. 8 Juan Martin del Potro of Argentina beat Gilles Muller of Luxembourg 6-7 (5), 7-5, 6-3, 7-5, remaining the only Argentine man still in the draw of the nine who started the tournament.
The 20-year-old del Potro won the Auckland title coming into Melbourne and is on a seven-match winning streak.
No. 19 Marin Cilic of Croatia had an upset 7-6 (5), 6-3, 6-4 win over No. 11 David Ferrer of Spain.
On the women's side, Olympic silver medalist Dinara Safina reached the fourth round for the first time in seven trips to the Australian Open with a 6-2, 6-2 win over No. 25 Kaia Kanepi of Estonia.
"There's a first time for everything. Twice I lost in the third round," the 22-year-old Russian said. "I was like this today: 'That is the third time. Should be the luckiest one.'"
The third-seeded Safina broke into the top 10 last year for the first time and credits having a full-time coach and trainer for the rise.
She has yet to win a Grand Slam singles title, although she reached the French Open final last year before losing to Ana Ivanovic of Serbia.
Fellow Russians Vera Zvonareva and Nadia Petrova are also in the fourth round.
No. 7 Zvonareva beat Italy's Sara Errani 6-4, 6-1 and No. 10 Petrova advanced when Kazakhstan's Galina Voskoboeva retired with back pain after losing the first set 6-1.
Safina planned to rest and return to Rod Laver Arena later Friday to watch older brother, Marat Safin, play second-ranked Federer.
"Well, I hope on center court with winning, I hope he can close the same way I win today," she said.
Safin, who beat Federer in the semifinals before winning the 2005 Australian title, looms as an obstacle to Federer's quest to equal Pete Sampras' 14 Grand Slam singles titles.
Security was tight across Melbourne Park for the Djokovic-Delic match. In 2007, police ejected more than 150 fans one day from the same area after hostilities escalated between ethnic groups.
Complaints about the cheering before and during points followed both Delic's previous wins over Taylor Dent and No. 28 Paul-Henri Mathieu.
He appealed to his fans for calm in a message on his website. Organizers took the precaution of putting the match on the all-ticket stadium.
Extra security staff were deployed to nearly packed stadium and kept a close eye on pockets of the most vocal fans.
There were significantly more Serbian supporters, but Delic had his share of backers, too.
When Delic broke for a 3-2 edge that was the key to taking the second set, he turned his hand toward his forehead, then pointed to his fans.
Djokovic pumped his fist and looked toward his most vocal supporters after getting the only break of the third set, when Delic whacked back-to-back double-faults to set up break point.
Otherwise, it was all business on court, punctuated by shows of good sportsmanship. Several times, Djokovic applauded with his racket after great shots by Delic and gave him the thumbs-up when the American correctly challenged a line call in the tiebreaker.