It was Williams’ second match since announcing she will “evolve away from tennis.”
Raducanu, the reigning US Open champ, now advances to the round of 32 with a 6-4, 6-0 win.
“I think we all need to just honor Serena and her amazing career. I’m so grateful for the experience, being able to play her and for our careers to have crossed over, and everything she has achieved is so inspirational,” Raducanu said on the court after the match. “It was a true honor to share the court with her.”
Williams, 40, did not speak on the court after the match Tuesday, leaving the court quickly. Williams also did not do a post-match press conference, according to Ben Rothenberg, a senior editor for the Racquet magazine and a CNN contributor.
Last week, an emotional Williams spoke to the crowd after a defeat against Belinda Bencic in the second round of the Canadian Open in Toronto and was adorned with gifts.
The 23-time grand slam winner is entered to play in the US Open, which starts later this month. And although she will try to win, Williams said in a Vogue article earlier this month that it’s time for her to move “in a different direction.”
“I have never liked the word retirement. It doesn’t feel like a modern word to me. I’ve been thinking of this as a transition, but I want to be sensitive about how I use that word, which means something very specific and important to a community of people,” Williams said in the article.
“Maybe the best word to describe what I’m up to is evolution. I’m here to tell you that I’m evolving away from tennis, toward other things that are important to me.”
She continued: “Unfortunately I wasn’t ready to win Wimbledon this year. And I don’t know if I will be ready to win New York. But I’m going to try.”
Williams has played in four singles matches this year: one at Wimbledon, two in Toronto and against Raducanu on Tuesday.
This was the first career meeting between the two players.
Williams’ daughter, Olympia Ohanian, was in attendance. So was four-time major champion Naomi Osaka, who lost in her first-round match earlier in the day.
According to the WTA, when Raducanu was born November 13, 2002, Williams had already won 18 titles, including four majors, and held the World No. 1 ranking for 18 weeks.
Raducanu, 19, is currently ranked 13th in the world and seeded 10th in this tournament. She is seeking her second career title.
Next, Raducanu will face another former World No. 1 in Victoria Azarenka.
“I think that at this level, you play anyone, it’s a really difficult match. Each of those wins kind of build confidence,” Raducanu told reporters after her win Tuesday. “But I’m not trying to get too high or too low right now. I’m just trying to stay on one path and trajectory.”
This is Raducanu’s debut in this tournament, while Williams is the only woman who has won back-to-back titles in this event in the Open Era, doing so in 2014 and 2015.
CNN’s Christina Maxouris contributed to this report.