U.S. former first lady Michelle Obama and tennis great Billie Jean King led the tributes to Serena Williams after her U.S. Open third-round loss to Ajla Tomljanovic on Friday, likely the final match of her sparkling career.

The 23-times singles Grand Slam champion's 7-5 6-7(4) 6-1 defeat sparked a flood of messages on social media, as current and former athletes across sport as well as the world at large celebrated her achievements of the last 25 years.

"Congrats on an amazing career, @SerenaWilliams! How lucky were we to be able to watch a young girl from Compton grow up to become one of the greatest athletes of all time," Obama said in a tweet.

"I'm proud of you, my friend - and I can't wait to see the lives you continue to transform with your talents."

Former world number one King, who watched on from the stands on Friday, later tweeted that Williams would remain in the spotlight.

"Her incredible career made its mark on tennis history. And yet her greatest contributions may be yet to come. Thank you, @serenawilliams. Your journey continues," King said.

Swimming great Michael Phelps hailed Williams not only for changing tennis but also empowering the next generation.

"Her tennis accomplishments speak for themselves, but one of the things I admire about her is she simply doesn't quit," the Olympic champion said.

"On or off the court her will, her strength, her determination... she simply never gives up. She’s a great example to us all."

Williams had credited Tiger Woods on Wednesday as one of the main reasons she was still playing tennis. The golf great, who watched her beat world number two Anett Kontaveit on Wednesday, showered her with praise.
Source: CNA