Top seed Venus Williams battled past Magda Linette to reach the quarter-finals of the Stanford Classic on Wednesday.
Williams needed three sets to get past her Polish opponent 6-3, 6-7(6), 6-2 in a match lasting two hours and 17 minutes.
The American claimed the first set with the only service break in the sixth game, after which the match went with serve until the ninth game when Williams saved two break points and went on to claim the opening set 6-3.
In the second, there were two service breaks apiece, including a titanic struggle in the eighth game when Linette broke serve by claiming it after her opponent saved four break points in a game with eight deuces. Thereafter things went with serve until the tie-break which Linette won 8-6, winning it after claiming it on her fifth set point.
In the third, Williams broke her opponent's serve three times to win the set and match 6-2.
In some other second-round action, third seed Johanna Konta if Britain hammered American Julia Boserup 6-3, 6-1 and in an upset unseeded Zheng Saisai of China downed French seventh seed Alize Cornet 6-4, 6-1.
Japan's fifth seed Misaki Doi saw off countryman Nao Hibino 6-3, 6-4 with two service breaks in the first set and one in the second to claim a fairly comfortable victory.