Germany's Angelique Kerber and Serena Williams after the match.

Saeed Khan / AFP / Getty Images

Angelique Kerber has upset Serena Williams in three sets to win the Australian Open title in a surprise victory.

The German tennis star defeated Williams 6-4, 3-6, 6-4, ending the six-time champion's unbeaten streak in finals at Melbourne Park, AP reported.

Williams was the favorite to win the Australian Open, where she had won all six previous times she'd reached the final, and was trying to equal Steffi Graf's Open-era record of 22 Grand Slam singles titles.

The 34-year-old Williams hadn't lost a set in the first six rounds here until dropping the first on Saturday night against No. 7 seed Kerber, who was playing in her first major final.