The skirt also holds symbolic meaning as it is built with six layers that honour Williams' "six previous title wins in Flushing."
The set's matching jacket and tote bag splashed in a deep midnight hue, and its light-refracting "crystal-encrusted bodice" mirrored the starry night sky, under which Williams played her match against Montenegro's Danka Kovinic on Monday evening.
The 23-time Grand Slam winner took the court in a pair of custom NikeCourt Flare 2 sneakers, featuring a "diamond-encrusted Swoosh design and her initials on the medial side" as well as gold lace deubres decorated with "400 hand-set diamonds in black ceramic created in collaboration with Serena Williams Jewelry," as per reports.
At yesterday's US Open, Williams won 6-3 against Montenegro's Danka Kovinic who is ranked 80th in the world. The 40-year-old also kept her first-round match win record flawless with this win, taking it to an impressive 21-0.
The packed to capacity Arthur Ashe Stadium erupted with support for the 23-time Grand Slam singles champion displaying a "We love Serena" sign. Before the match, the stadium watched a video montage celebrating what Williams has achieved as a player and a person.
After the match, Williams received a standing ovation and remained on the court for the US Open's video tribute narrated by Oprah Winfrey.
Earlier this month, the 40-year-old had revealed in an essay published in Vogue magazine that she will likely walk away from the sport after the US Open.