The 39-year-old champion donned a black, red and pink, one-legged catsuit with bright sleeves and a Nike compression fabric running down her right leg, and looked incredible in it.
But of course, in true Williams fashion, the outfit wasn't just her trying something different, it was specifically designed to pay tribute to one of her heroes: sprinter Florence Griffith Joyner, whose 1988 Olympic trial records for the 100-metre and 200-metre sprint still stand today.
As well as being known for her history-making athletic ability, Flo-Jo was also well-known for the brightly-coloured and memorable outfits she designed herself while tearing around the track. You might recall Beyoncé recreating the iconic look for Halloween in 2018.
Not only did Griffith Joyner set those two world records in 1988, but she also won three gold medals for the 100-metre, 200-metre, and 4x100-metre events. When asked about her style in a 1992 interview, Griffith Joyner said that fashion had been a part of her life since she was a young child.
"Track and field is a beautiful sport, and I just wanted to bring in my personality and the clothes that I wear off the track, onto the track, just to be myself" Griffith Joyner said.
"I was inspired by Flo-Jo, who was a wonderful track athlete," said Williams in her post-match interview on Monday. "Watching her fashion, just always changing, her outfits were always amazing."
It just happens to be the cherry on the cake that destroyed the game, scoring 6-1 6-1. Like we said... iconic.