Andre Agassi may be the great entertainer of tennis but even he knew the show had to end some time.

The American has performed one of the greatest encores in modern sport, winning three of his four Australian Open titles since turning 29, long after his contemporaries had taken their final bows.

But the curtain had to fall eventually and it did on Thursday when he was beaten by Russian Marat Safin 7-6, 7-6, 5-7, 1-6, 6-3 in the semi-finals.

It was Agassi's first loss at Melbourne Park in 27 matches dating back to 1999 and he felt the pain sharply.

"It's definitely the toughest day I've had," Agassi said. "It was really close but I felt like I could never quite get over that hump."

The 33-year-old Agassi knows his chances of adding to his eight Grand Slam titles are beginning to fade.

He is not planning to retire quite yet but like any gambler who visits his home town of Las Vegas, he is starting to hedge his bets.

Instead of giving the crowd a customary wave before returning to the locker room after losing to Safin, Agassi strolled back on to centre court, bowed his head and flashed his famous smile.

"You never know when it's your last, so you want to say bye properly," he explained.

"I have no plans to (retire) but, you know, a year's a long time."

Agassi's career already reads like a Hollywood blockbuster. A prodigious talent who won the biggest prize in the sport then threw it all away, he staged an unlikely comeback to complete his set of all four Grand Slam titles and become the oldest world number one in history.

A broken marriage and a successful one to former tennis champion Steffi Graf, with whom he has had two children, could not stop the American in his tracks but Safin may have.

Agassi described the loss as more painful than any he had suffered against his great nemesis Pete Sampras, and the fact he was agonisingly close to beating the brooding Russian only made it worse.

He recovered from losing of two close tie-breaks to force the match into a fifth set, only to run out of gas against a man nine years his junior.

"It was really close," Agassi said. "That match could have been straight sets -- both ways.

"I felt like I had the momentum but when a guy has a weapon like that...he can get through so many games without sort of spending that energy and hitting those crucial nervous shots.

"It was a tough one today. Marat played at an incredibly high level and he came up with a lot of great shots when he needed to. I hate it when he does that."