The 23-time Grand Slam champion sported an all-black bodysuit with a red waistband for her 7-6, 6-4 victory against her Czech counterpart. Williams, 36, is playing in the tournament unseeded, due to her ranking of 453 before the tournament. She moved up to No. 451 with the win. Pliskova is ranked No. 70 by the Women's Tennis Association.
Williams' black Nike garb stood out among a field clad in skirts and dresses. The outfit also drew a wide range of reviews on social media, with many users likening the former world No. 1 to a superhero.
"Catsuit anyone? For all the moms out there who had a tough recovery from pregnancy -- here you go," Williams wrote on social media. "If I can do it, so can you. Love you all!!"
Williams battled back from a 3-0 deficit in the tie-break to take the first set. She won match point after Pliskova hit the top of the net on a return.
"I feel like a warrior in it, like a warrior princess kind of, [a] queen from Wakanda," Williams said on the Tennis Channel.
"I'm always living in a fantasy world. I always wanted to be a superhero, and it's kind of my way of being a superhero. I feel like a superhero when I wear it."
Serena was playing in her first Grand Slam match since beating Venus in two sets on Jan. 28, 2017 in the Australian Open final.