Serena Williams's comeback stalled when she suffered a surprise 6-2, 6-3 defeat by Russian Nadia Petrova in the quarter-finals of the Amelia Island championship on Friday.
Williams, who returned to competition after an eight-month injury lay-off to win the Nasdaq-100 Open last week, committed 42 unforced errors and failed to convert any of her 10 break-point opportunities at the $585,000 event in Florida.
Seventh seed Petrova capitalised on the rustiness of the former world number one to triumph in one hour 17 minutes and set up a semi-final with Lindsay Davenport.
Fourth seed Davenport made light work of finishing off her delayed third-round match from Thursday night, taking two games to beat Australian Alicia Molik 6-4, 7-5.
The American then returned to oust Argentine Paola Suarez 6-4, 6-1 in the quarter-finals.
Williams's defeat means the anticipated first meeting of the year with world number one Justine Henin-Hardenne
The Belgian kept up her end of the bargain, overcoming Russian eighth seed Vera Zvonareva 6-4, 6-3.
But Henin-Hardenne was far from comfortable, saving five break points in the first set.
She will meet third seed Amelie Mauresmo in Saturday's other semi-final after the Frenchwoman beat Italian 10th seed Silvia Farina Elia 6-4, 6-3.