Briton Raducanu had never before faced the legendary Williams until her encounter at the Western & Southern Open, in which she earned a classy 6-4 6-0 triumph.
With 23-time singles grand slam winner Williams recently announcing the upcoming US Open will be the final tournament of her glittering career, the chance for Raducanu – the defending champion at Flushing Meadows – to go toe-to-toe with one of her idols was running out.
The match in Cincinnati is one she will not forget in a hurry.
"It feels pretty amazing, to be honest. I can't believe I just played Serena Williams," Raducanu said.
"[This] may be one of the last opportunities I get to play her. You have to cherish the moment, and you're going to have this memory for the rest of your career.
"I was just really trying to make the most out of every single point out there and give myself the best memories of when I played Serena once."
There were no exuberant celebrations from Raducanu despite the impressive manner of victory against a player many consider to be among the best to have ever played the sport.
Raducanu explained that was out of respect for the 40-year-old.
"To be honest, I was just in awe. I think I said one 'come on' in the match, and I was just saying [it] to myself, because I respect her so much as an athlete, as a tennis player, as a person," she added.
Unlike last week in Canada, when Williams stayed behind for a rare on-court interview after a defeat, there was little fanfare in Cincinnati, as she hastily exited and opted to not speak to the media at all.
The day when fans no longer get to witness a true sporting great grace the court is growing ever nearer, and Raducanu says everyone needs to appreciate the final few weeks of Williams' illustrious career.
"I think we all need to just honour Serena and her amazing career," she added.
"I'm so grateful for this experience to play her and for our careers to have crossed over. Everything she achieved is inspirational and it was a true honour to share the court with her."
Raducanu next faces another former world number one and grand slam champion in the form of Viktoria Azarenka.
"Obviously with the last year I have had, getting great exposure to these great players, and every time you get to play them, you get to learn from them as well and what they do really well that has helped them in their careers," she said.
"Yeah, it's going to be a tough match, for sure."