Six-time champion Serena Williams battled through a challenging three-set test against Greek 15th seed Maria Sakkari to reach the US Open quarter-finals.
Williams, 38, looked composed as she took the first set in 37 minutes.
The third seed lost a close tie-break in the second and was forced to find her best tennis to come from a break down in the third and win 6-3 6-7 (6-8) 6-3 almost two hours later.
“I just kept fighting,” Williams said.
“She was doing so well. She was being so aggressive and I knew I needed to do the same thing.”
Williams’ next opponent is Bulgaria’s Tsvetana Pironkova, who has never reached the US Open quarter-finals before and is playing her first tournament since Wimbledon 2017.
Pironkova beat French world number 56 Alize Cornet 6-4 6-7 (5-7) 6-3.
The American is seeking a 24th Grand Slam singles title as she attempts to equal Margaret Court’s record.
Williams had initially looked vulnerable when she went a set down in her third-round match against Sloane Stephens and again it was Sakkari who had the faster start.
The pair had met two weeks previously in the last 16 of the Western and Southern Open, when Williams let a set and break lead slip to lose.
The seven-time Wimbledon champion was threatened when Sakkari set up three break points at 2-2 in the first set, but the Greek could not take the early opportunity.
The momentum changed hands as Williams dominated a rally with pacy forehands to break the world number 22’s serve at the third attempt.
And an ace down the middle sealed a hold to love to give the American the first set.
Williams’ serve saved her on several occasions, reaching 124mph at one point. Sakkari had a chance to break at 3-2 and 40-40 in the second set, but Williams slammed the door shut with two aces.
And the seven-time Australian Open champion was just as powerful from the baseline, with an incredible forehand overwhelming Sakkari and switching the momentum in the seventh game.
The Greek upped her intensity to meet Williams’ level and a net cord in her favour gave Sakkari set point and elicited a pained cry from Williams.
More impenetrable serving saved that and a second set point, taking it to a tie-break.
An 89mph forehand and another booming backhand saved a further two set points for Williams, but eventually her forehand sailed wide to give Sakkari the set.