Serena Williams has given birth to a baby girl at a clinic in Florida, the first child for the former world number one tennis player, her coach Patrick Mouratoglou said on Twitter on Friday.
Williams, 35, whose partner is Reddit co-founder Alexis Ohanian, was admitted to the St Mary's Medical Center in West Palm Beach on Wednesday, as per reports by the BBC.
The Tennis star has not competed since winning the Australian Open in January but has posted several videos to social media showing her hitting balls during her pregnancy, according to Channel NewsAsia.
Williams, the world's highest-paid female athlete, was about two months pregnant when she captured her 23rd Grand Slam singles title at the Australian Open, one short of the all-time record held by Australian Margaret Court.
The 23-time Grand Slam winner said last month she was planning to return to tennis for the Australian Open in January.
Congratulations have been pouring in from sports stars and celebrities.
Fellow American Sloane Stephens said she expected to see a lot of the newborn.
"I am very happy for her," she said. "I cannot wait to see the little baby girl on tour because I am sure she will be around."
"Obviously I'm super-excited," Venus Williams said. "Words can't describe it", as reported by the New York Times.
The couple is yet to confirm the birth themselves but Serena's coach, Patrick Mouratoglou, tweeted: "I am so happy for you and I feel your emotion."
He added: "Btw ... I wish you a speedy recovery... we have a lot of work ahead of us."
Serena admitted she had revealed her pregnancy to the world in April by accident, after mistakenly uploading a photograph on Snapchat.
In an article in Vogue last month she said she wanted to defend her title.
"It's the most outrageous plan," she said. "I just want to put that out there. That's, like, three months after I give birth."
Rafael Nadal was amongst the first to tweet his congratulations.
At a news conference, world number threeGarbineMuguruza joked; "a baby girl? Well, I hope she doesn't play tennis," Reuters reported.
Singer Beyonce posted a portrait of a pregnant Williams on Instagram, with the message: "Congratulations Serena!"