On July 10, Sugiyama reached the final of the women's doubles at Wimbledon, partnered by Julie Halard-Decugis, but lost in straight sets to sisters Venus and Serena Williams 3–6, 2–6 after a one-day rain delay. On September 10, Sugiyama won the women's doubles at the US Open, defeating Cara Black of Zimbabwe and Russian Elena Likhovtseva 6–0, 1–6, 6–1 in one hour and 19 minutes. On October 23, she became the first Japanese woman to rank No. 1 in the world in doubles, winning seven titles in the process.