Federer and Williams both won their earlier singles matches as well.
"It was great fun. I really enjoyed playing against Serena. What an honour," 20-time Grand Slam winner Federer said after the match.
"I was nervous returning because people talk about her serve so much. I know why they say it now, she has a wonderful serve.
"She's a great champion, you see how focused she is and I love that about her."
Federer and Swiss teammate Belinda Bencic beat Williams and Frances Tiafoe. Credit: PA
Williams added: "It was so fun. This is super cool that we get to do it at such a pinnacle point of our careers.
"This guy is great, both off the court and on the court. I think his serve is super-underestimated. It's a killer serve, you can't read it. I watched him all the time and I never knew how amazing it was."
Federer and Williams' historic match saw the two play against each other for the first time.
Ahead of the day, Federer said the prospect of playing with Williams was 'very exciting' for both of them, as he had a lot of respect for her both within the sporting world and outside of it.
"I hope a lot of tennis fans will tune in to watch the match, because it's going to be one time and probably never again in this kind of a competition," he explained.
"I admire everything she's done on and off the court. We can relate to one another now even more so for being parents.
"I've played with some of the greatest doubles players in the world in Martina Navratilova and Martina Hingis, and I've also played against some of the best in Venus [Williams] and other great ones in the past.
"This time it's against Serena, who is one of the biggest champions ever in our sport - men and women combined."
The two tennis icons played together for the first time and took a selfie to mark the historic moment. Credit: Instagram
Williams also admitted she was hell-bent on getting a selfie with Federer to share with her 10.3 million Instagram followers.
She may not have won the match, but she thankfully did succeed in securing that selfie - marking the historic moment in the modern way that we're all used to.
Featured Image Credit: PA