Federer and Microsoft founder Gates beat Jack Sock and NBC Today show host Savannah Guthrie 6-3.
The 16,000 strong crowd in San Jose, California were treated to some entertaining tennis.
At one point, Federer dropped to his knees as he exchanged a volley rally with Jack Sock at the net.
After the match, Federer was congratulated on winning his 20th Grand Slam title and returning to the top of the world rankings.
The Swiss legend looked moved as he opened up on his achievement.
When asked what he meant, he said: “It was definitely special times in my life and career.
“The dream as a little boy was maybe one day to be World No 1, but not at 36!
“It was at some point at 25 maybe if things went really well.
“I had a tough year in 2016 with my knee, stayed positive and was resilient.
“I fought to come back and really believe I could win again.
“I didn’t think it was going to be at this level, but it’s been an unbelievable journey the last 14 months.
“My team has been incredible and loving every moment I can stay on Tour.
“You never know when it is going to end.
“For me to stand here in San Jose as world No 1 is very special for me.”
Federer then took on Sock in an exhibition singles match which is best of three sets.
The 36-year-old’s charity, the Roger Federer Foundation, put on the event to help raise awareness of and fight child poverty in Africa.