The 23-time Grand Slam champion beat her big sister, Venus Williams, 6-1, 6-2 in their highly-anticipated matchup on Friday at the U.S. Open in Queens.
The sisters — Serena seeded 17th and Venus 16th — played each other in the third round of the Grand Slam tournament.
Serena, 36, beat out Venus, 38, with 2-0 in sets and will now move on to the round of 16.
Serena Williams, who had a medical timeout in the first set, will play Estonia’s Kaia Kanepi in the last 16.
The American siblings, aged 38 and 36, were playing for the 30th time since they first competed against each other 20 years ago.
“This was my best match since I have returned. It’s not easy,” Serena said of beating her big sister Venus in an interview after the match.
“She’s my best friend, she means the world to me. She’s so supportive of my career and I’m extremely supportive of her career and every time she loses I feel like I do.
So yeah, it’s not very easy, but it’s a tournament and we all know that there’s more to life than just playing each other and playing tennis.”
Venus said she thought it was her sister’s best performance in their matches, because she did not “even get to really touch any balls”.
“I don’t think I did a lot wrong. But she just did everything right,” Venus told a news conference.
“Obviously, that level is definitely where she’s going to want to stay during this whole tournament.”