In this great clash tennis was the true victor as two of the game's stars were treated by fans worldwide to witness an unforgettable evening.
In the end, the Swiss team came out on top, 4-2, 4-3 (3), playing under the Fast4 format.
"It was great fun. I'm really happy", Federer said.
"I was nervous returning because people talk about her serve so much". I wanted to take pictures and I wanted bring my baby out.
Williams and Federer, both 37, have shared the court when winning Grand Slam titles on the same weekend eight times, most recently in 2017.
"This was a great start but obviously a long way to go here and in Melbourne", Federer said.
"I felt a bit uncomfortable in the first match I played".
Serena: 'The guy is great. He's the greatest of all time. There's a reason why he's the greatest, because you can't be that great and not have such an awesome weapon like that serve. He has a killer serve. "I watched him all the time and I never knew how fantastic it was", she added. "Hopefully, I can get some tips later!"
Williams boasts 23 major titles, with her last coming at the Australian Open in 2017.
Tennis fans may get a small taste of evidence to prove or disprove McEnroe's theory with the upcoming Hopman Cup. "We try our best".
At the annual Hopman Cup New Year's bash, the duo showed their great friendship as they rang in the start of 2019.
Roger Federer emerged triumphant from a historic first meeting with Serena Williams in the Hopman Cup Tuesday, but tennis was the true victor as two of the game's greats treated fans worldwide to an unforgettable evening.
Even though it's the first time they've been on the same court, it's not the first time they've spoken so highly of each other.
After the match, Williams told the crowd she was "kinda sad the match was over". "I have been looking forward to it". I think his serve is super-underestimated.
"As a player it's something that you would dream of, to play Roger Federer". Federer has lost just seven games in his first two matches of the round-robin tournament.
"We're both fierce competitors and we always want to win. You're a superman over there because it's hard with just one", she said. "It was great to be back out on match day".