Marat Safin sent out a warning to his Australian Open rivals in Melbourne by ousting top seed Andy Roddick in the quarter-finals.
The Russian, back to form after injury, claimed an enthralling 2-6 6-3 7-5 6-7 6-4 win to mark his 24th birthday.
Safin made the crucial break at 4-4 in the final set, and served out the next game to clinch the match.
The former US Open champion will now face defending champion Andre Agassi in the semi-finals.
"Roddick started really well and he's improved a lot since the last time we played," said Safin.
"He serves so well, his backhand is great and his forehand is one of the best in tennis and it is tough to hold it on the baseline with him.
"But now I am back and that is the most important thing for me."
Roddick added: "He played great tonight... I have to just suck it up and give credit to him."
It looked as though it would be business as usual for Roddick as he easily broke Safin in the second game and again in the sixth take the opening set 6-2.
But the world number one lost some of the psychological edge when the unseeded Russian sought advice for a thigh injury at the changeover.
Safin seemed to be energised by the hold-up and broke Roddick in the third game with some impressive ground strokes, going on to level the match.
The crowds in Melbourne were then treated to a fast and furious display of thudding serves and intense rallies.
This time Safin had to wait until the 12th game to pounce on some rash mistakes by Roddick to steal the third set.
The match was even tighter in the fourth, but the top seed used his trademark serve to great advantage storming to the tiebreaker 7-0.
A tense fifth set followed the same pattern as neither player gave the other an inch until the ninth game.
A lapse in concentration saw Roddick net a backhand at 15-40 before he tapped a forehand volley into the net to gift Safin the break.
The Russian dug deep to battle back from 15-40 in the next game before sealing the match with a pair of forehand winners.
And Safin, who left the court to choruses of 'Happy Birthday To You', had given himself the best 24th birthday present - a place in the semi-finals.