Throughout her decades-long career, she dominated and revolutionised the women's game, winning 23 Grand Slam singles titles.
"Just keep supporting me," Williams said after the match, "as long as I'm here."
"With her tremendous serve, return of serve, and agility, she truly set that bar in the women's game."
Serena Williams received tributes from fellow athletes and fans as she prepared to hit the court on Monday, including a position on the cover of Time magazine.
In singles, Williams is currently ranked 605th in the world.