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 for an eventual 6-3 6-7 (6-8) 6-3 win almost two hours later.
Williams plays France’s Alize Cornet or Bulgaria’s Tsvetana Pironkova next.
The American is seeking a 24th Grand Slam singles title as she attempts to equal Margaret Court’s record.