Third seed Serena Williams advanced to the US Open quarter-finals after a gritty, tension-filled 6-3 6-7(6) 6-3 win over Greece's Maria Sakkari.
Early nerves saw Williams start with a double fault, but the veteran then found her footing, playing strong defensive tennis to save all three break points against her in the first set.
"I just kept fighting," she said. "She was doing so well. She was being so aggressive and I knew I needed to do the same thing."
Meanwhile, second seed Dominic Thiem edged a first-set tiebreak before turning up the heat to romp into the quarter-finals with a resounding 7-6(4) 6-1 6-1 victory over Canadian youngster Felix Augur-Aliassime.
Top seed Novak Djokovic's disqualification on Sunday for striking a line judge with a ball has left Thiem as one of the favourites and the Austrian gave a composed performance to reach the last eight in New York for the second time in his career.