World number one Roger Federer edged ahead of Andre Agassi 6-3 2-6 7-5 before rain interrupted their US Open quarter-final on Arthur Ashe court.
The Swiss competently took the opening set but the veteran American countered with his powerful play from the baseline to level the match.
Federer recovered to take the third set before rain left the match poised at 40-40 in the first game of the fourth.
The number one seed is tied 3-3 in head-to-heads with the 34-year-old.
Agassi seemed woefully off pace in the opening stages of the match on Arthur Ashe Court.
A sharp-looking Federer, who has not played a match in four days, fired down three aces in his opening game.
Agassi handed the Swiss a break and a 4-2 lead when he pushed a forehand wide after a long rally.
The sixth seed survived two set points at 5-3 but Federer held serve, polishing off the opening set in 30 minutes.
The tide turned in the second set as Agassi got the measure of the world number one's serve.
The double US Open champion raced to a 3-0 lead and made no unforced errors in the first five games.
He broke the top seed again to claim the set with a cross-court winner that received a standing ovation.
But Agassi's resolve faltered in the third set as two mistakes handed Federer the break at 6-5.
The Swiss ruthlessly sent down three service winners to move ahead again in the match.
Rain began to fall once more, leaving Agassi clinging on to deuce on his serve in the opening game of the fourth set.