Venus Williams continued her disappointing start to the year when she suffered a 6-2, 6-3 defeat by Russia's Svetlana Kuznetsova in the quarter-finals of the Dubai Open on Thursday.
World number one Justine Henin-Hardenne took just 48 minutes to sweep aside an ailing Conchita Martinez 6-1, 6-0.
Second seed Williams was absent from the tour after Wimbledon because of injury and has struggled since returning at the Australian Open.
She lost there to compatriot Lisa Raymond in the third round, and then won just one match in Tokyo before defaulting her quarter-final because of a knee injury.
Kuznetsova, 18, used a big forehand, solid serve and strong groundstrokes to keep the American under pressure, and after dropping her serve in the opening game looked the more solid player.
Williams showed a few glimpses of her ferocious groundstrokes, notably when she held serve to love after falling behind a set and 3-0.
The American briefly threatened a comeback, pulling back to 2-3, but made far too many unforced errors and three more consecutive breaks of serve left Kuznetsova serving for the biggest victory of her young career.
"I played great today. I was relaxed and tried to play my game," she said. "I really enjoyed it today."
"She's not at the top of her level now, but when you play against these top players you still have to play so good to beat them," said Kuznetsova, who trains at the Emilio Sanchez academy in Spain.
Williams has won just four matches in three tournaments this year.
Henin-Hardenne found little resistance from Martinez, who was suffering from a neck strain.
The eighth-seeded Spaniard looked lethargic and was slow to go for the wide ball, and at the end of the first set received lengthy treatment. It proved to be ineffective and she barely competed in the second set.
"It's never easy to play against somebody who is injured and is not moving that well," said Henin-Hardenne, "and Conchita is always a problem for a lot of players.
"She doesn't give any rhythm, and I just tried to stay focused on every ball and that worked pretty good."
