Serena Williams' long winning streak came to an end in a stunning fourth-round defeat to Ana Ivanovic at the Australian Open on Sunday. Ivanovic hadn't won a set in her four previous matches against Williams, who had been a hot favorite to win a sixth Australian Open crown for her 18th Grand Slam title. Williams later admitted she'd been bothered by a back problem in practice in recent days and considered pulling out of the tournament. The No. 14-seeded Ivanovic set up the 4-6, 6-3, 6-3 win by attacking the best serve in women's tennis. More...