Williams, seeking the first singles medal of her career, has lost 13 games through four rounds. She'll face top-ranked Victoria Azarenka on Friday for a berth in the final.
Playing on sun-splashed Court 1 at Wimbledon, Williams swept the first seven games against the No. 8-seeded Wozniacki. Williams kept one rally going with a desperation, off-balance left-handed shot, but lost that point and the game.
Otherwise Williams stuck to the basics. She has won 11 consecutive matches this summer at the All England Club, including her fifth Wimbledon title a month ago.