It's the end of an era.

Serena Williams lost her third-round match at the U.S. Open on Friday in three sets to Alja Tomljanovic, capping off her illustrious career.

Williams took a commanding 5-3 lead in the first set, well on her way to make the third round look easy. However, she lost four games in a row and lost the first set 7-5. 

But she came back with a vengeance in the second set. In fact, she utterly dominated early on.

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She answered by winning the first four games of the set, but Tomljanovic didn’t go down quietly. She won the next two games, and even came close to breaking Williams’ serve again, but the 23-time grand slam champion refused to let that happen. At deuce, she earned back-to-back points to clinch the game.

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But once again, Tomljanovic battled back. She won the next three games to tie the set at five – one game took over 15 minutes to complete. They exchanged games to go into a tiebreaker, which Williams won 7-4 to bring the match to a decisive third set.

Momentum stayed on Williams' side to begin the third set, as she broke the Australian’s serve to win the first game. 

But down 40-15 in the second game, Tomljanovic fought back to break Williams' serve. From then on, Tomljanovic dominated, but Williams wanted her career to keep on going. There were eight deuces and six match points as Williams trailed 5-1, but Tomljanovic finally got the job done, winning six straight games to end the match and Williams' career.

Williams and her sister, Venus, lost in the first round of the women's doubles tournament on Thursday.

Williams retires with 23 grand slams - seven Wimbledons, seven Australian Opens, six U.S. Opens, and three French Opens - the second-most of all time.