Agnieszka Radwanska is through to the last 16 at Indian Wells after Jamie Hampton was forced to retire in the deciding set of their match.
The Polish fifth seed had looked to be on course for a comfortable victory as she took the opening set 6-3.
World number 99 Hampton, who had claimed only one game on the pair's only previous meeting in Stuttgart, caused a shock by taking the second 6-4.
With the American 3-0 down in the decider, she ended the battle, sending Radwanska through to face either Julia Goerges or world number one Victoria Azarenka in the next round.
Illness at the tournament has now accounted for the exits of eight players, including Vera Zvonareva and Gael Monfils.