It's almost game, set, match for the tennis champ.

Serena Williams has kicked off her final US Open campaign, the last tournament of her tennis career – and naturally, all her celebrity friends wanted to cheer her on.

The likes of Anna Wintour, Rebel Wilson, and Gayle King dressed in their finest outfits to attend Day One of the tournament in Queens, New York.

But Williams was not to be outdone in her custom-made tennis attire.

Scroll through to see the outfit and the other stars who showed their support courtside.

Serena Williams hit the court in style on August 30 (August 29 US time) in the first round of her last ever US Open.

To mark the occasion, the champion had diamond-encrusted shoes made especially for the big day. That's right, Williams had Nike fit 400 hand-set diamond stones adorn her footwear as the words "Queen" and "Mama" in solid gold tags sat flush against the shoelaces.

And her outfit is custom-made too. The star wore a six-layer skirt – with each layer representing the number of times she won the US Open title.

Aussie actress Rebel Wilson and her girlfriend Ramona Agruma were on hand to celebrate Williams' milestone moment. The couple took a quick boomerang for Instagram ahead of the Round 1 match.

Gayle King has always been a Serena Williams fan, so it was no surprise she was at the game. But first, the American journalist posed for pics against a photo wall outside the courts in Flushing, Queens.

Vogue editor-in-chief Anna Wintour was also on hand to lend her support – and bring her sartorial star power courtside.

American TV and media personality Katie Couric was all smiles in her sundress before heading courtside for the game.

It was a family affair for director Spike Lee, who took his Jackson Lee to Day One of the US Open to cheer on Serena Williams.

American skier Lindsey Vonn was also there to support her fellow athlete. Vonn would know exactly how Serena Williams is feeling in her farewell tournament as not too long ago, Vonn announced she would retire after the 2019 World Championships.

Serena Williams has supported designer Vera Wang many times, wearing her designs to events and awards show in the past. Now it was Wang's turn to return the favour, sitting at USTA Billie Jean King National Tennis Center to cheer on the tennis champ.

Singer Anika Noni Rose was given the privilege of performing the US national anthem prior to the match between Serena Williams and Danika Kovinic of Montenegro.

We're used to actor Anthony Anderson joking around on and off set. But when it comes to the court, he brings his game face.

There's no denying Serena Williams has friends in high places – she even counts former US President Bill Clinton as an ally. The retired politician looked animated as he watched the tennis ace play on centre court.

From one queen to another! Actress Queen Latifah was in good spirits and sending Serena Williams good vibes only from the stands.

Mike Tyson was among the 24,000-strong crowd who watched Day One of the US Open, when Serena Williams beat World No. 80 Danka Kovinic in straight sets.

Tennis great Billie Jean King was among the first to congratulate Serena Williams for her win in the first round.

"She has been an amazing representative, a fantastic leader helping women, particularly of colour," King wrote in an op-ed for the New York Times on August 29 before the 2022 US Open launch.

"She's not afraid to speak her truth. Serena Williams plays today. I'll be watching and cheering her on."

From the press wall to centre stage, Gayle King was one of the lucky ones to get up close to Serena Williams.

In a post-match interview, the tennis star thanked King and the crowd for their support.

"The crowd was crazy," she said. "It really helped pull me through. I was really pumped, I was like, Yes, I got this.'"