With no ranking, Clijsters needed wild cards to begin her comeback. She requested and received wild cards for the Cincinnati Open, the Canadian Open, and the US Open. In her return to the tour in Cincinnati, Clijsters defeated three top 20 opponents, including No. 6 Svetlana Kuznetsova, before losing to world No. 1 Dinara Safina in the quarterfinals. She recorded another top ten victory in Canada over No. 9 Victoria Azarenka. Clijsters was still unranked entering the US Open, as players needed three tour events to have a ranking at the time. Nonetheless, she made it to the final, notably upsetting both Williams sisters, No. 3 Venus in the fourth round and No. 2 Serena in the semifinals. She defeated Venus in a tight third set after they split the first two 6–0. Her straight sets win over Serena was overshadowed by her opponent receiving a point penalty on match point for verbally abusing a line judge. Clijsters then defeated No. 8 Caroline Wozniacki to win her second US Open championship. She became the first unseeded woman to win the title at the event, and the first mother to win a Grand Slam singles title since Evonne Goolagong Cawley in 1980. With the title, she entered the WTA rankings at No. 19. Her only other tournament of the year was the Luxembourg Open, where she lost her second match. At the end of the season, she won the WTA Comeback Player of the Year award for the second time.