Venus Williams battled to a dramatic 4-6, 7-5, 6-4 victory over Martina Hingis on Thursday to reach the quarter-finals of the Warsaw Cup.
American Williams, who has been taking medication for a throat infection, suffered cramps in the final set and could barely move at the end.
Hingis had every opportunity to win the two hour 38-minute battle and the nightmare of her struggle to get the better of the Williams sisters, which many in the game believe played a part in her retirement in 2002, re-emerged.
A strong wind prevented both players from producing their best tennis and Swiss Hingis came within two points of victory at 5-4 in the second set.
Although Williams held for 5-5 and conceded just two points in the remainder of the set, cramps struck her when she had broken to lead 1-0 in the third set.
She received treatment at 1-1 after dropping her serve, again after breaking to love to lead 2-1, and once more when leading 3-2.
When Hingis, like Williams a former world number one, broke her to love to level at 3-3 it appeared as if the American's challenge was over.
Barely able to lift off to serve, or to move, she relied on hitting out as hard as she could at any ball that came within reach.
Her big forehand had already given Hingis major problems, and there were enough of them in the desperate last stages to prevent the Swiss taking control.
The power of her opponent forced Hingis into errors, and after an exchange of breaks to 4-4, a forced backhand error gave Williams another break for 5-4 and she served out for the match.