Serena Williams was pushed hard by fifth seed Simona Halep before coming through in three sets to to reach the semi-finals of the US Open in New York.
The American six-time champion won a gripping contest 6-2 4-6 6-3 in the Flushing Meadows night session to close in on a 23rd Grand Slam singles title.
Williams, 34, will play Czech 10th seed Karolina Pliskova in the semi-finals at 00:00 BST on Friday.
They will be followed by Angelique Kerber against Caroline Wozniacki.
Williams and Kerber are battling for the world number one ranking, with the American knowing that, to hang on to top spot, she must reach the final.
Should the German second seed line up as her opponent on Saturday, Williams will have to win the title.
I needed to step it up – Williams
It took the best part of two hours for Williams to break free of the tenacious Halep with a succession of heavy returns giving her a 3-1 lead in the final set.
Williams had dominated the first set with six aces and three breaks of serve, but Halep had become the first woman at this year’s US Open to break the American’s serve, and she posed a greater challenge in the second set.
The Romanian fought off 12 break points and converted her fifth set point of an epic 10th game to draw level, and a huge shock loomed when she stood at 15-40 early in the second set.
Williams clung on, however, winning three straight games to build a lead she would not relinquish.
“I knew that I could play a lot better,” she said of being taken to a deciding set.
“I lost my rhythm a little in the second set and Simona kept playing really well, going for her shots, but I knew if I wanted to win this I needed to step it up in the third set.”
Pliskova, 24, beat Croatian teenager Ana Konjuh 6-2 6-2 to reach the last four of a Grand Slam for the first time.
She did not face a break point and dropped only five points on her serve as she swept past the 18-year-old in just 57 minutes.
“It’s an amazing feeling,” said Pliskova. “I am so excited to be in my first semi-final, especially in this tournament. I very much love New York and hard-court season.”
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