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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 plays French world number 56 Alize Cornet or Bulgaria's Tsvetana Pironkova - playing her first tournament since Wimbledon 2017 - next.
The American is seeking a 24th Grand Slam singles title as she attempts to equal Margaret Court's record.