Related news: Reactions after Serena Williams' U.S. Open defeat

FORMER U.S. FIRST LADY MICHELLE OBAMA "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. I'm proud of you, my friend -- and I can't wait to see the lives you continue to transform with your talents."

FORMER TENNIS WORLD NUMBER ONE BILLIE JEAN KING "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."

GOLF GREAT TIGER WOODS "@serenawilliams you're literally the greatest on and off the court. Thank you for inspiring all of us to pursue our dreams. I love you little sis!!!!!!"

AUSTRALIAN TENNIS PLAYER AJLA TOMLJANOVIC "I'm feeling really sorry just because I love Serena just as much as you guys do. What she's done for me, for the sport of tennis, is incredible. "I never thought I'd have a chance to play her in her last match when I remember watching her in all those finals, so this is a surreal moment for me. "I thought she would beat me, so the pressure wasn't on me. Even to the last point, I knew she's in a position to win even when she's down 5-1. That's just who she is and she's the greatest of all time. Period."

22-TIMES TENNIS GRAND SLAM CHAMPION RAFA NADAL "She's an inspiration for a lot of people around the world. She gave a lot to tennis so we are lucky to have had such a great ambassador like Serena for such a long time. "She deserves to choose whatever fits for her at this stage of her life. So I wish her all the very best and hopefully we can keep enjoying her around the Tour."

FOUR-TIMES GYMNASTICS OLYMPIC GOLD MEDALLIST SIMONE BILES "Thank you @serenawilliams for transcending sports for black athletes, female athletes and every athlete. Such a pleasure to watch, thanks for being an inspiration."

OLYMPIC SWIMMING CHAMPION MICHAEL PHELPS "It's truly been fun to watch Serena not only change the sport of tennis, but more importantly, how she's helped empower the next generation. "Her tennis accomplishments speak for themselves, but one of the things I admire about her is she simply doesn't quit. On or off the court her will, her strength, her determination ... she simply never gives up. She's a great example to us all."

AMERICAN TENNIS PLAYER COCO GAUFF "Serena, THANK YOU. It is because of you I believe in this dream. The impact you've had on me goes beyond any words that can be put together and for that I say thank you, thank you, thank you, GOAT!"

FORMER DOUBLES TOP-10 TENNIS PLAYER VANIA KING "It has been an honour to watch Serena as a child, to play on the same Fed Cup team as a 17-year-old, compete against her on the biggest stage of our sport (and bring Beyonce and Jay-Z to watch me), and as GOATs do, finish her career years after mine."

FOUR-TIMES NBA CHAMPION LEBRON JAMES "You're a GOAT. What you've done for the sport, what you've done for women ... is unprecedented. It was an honour to watch your journey, to watch you conquer all the goals you ever set, to see you break records, to see you just be amazing on the tennis court and also off it."

FORMER TENNIS WORLD NUMBER ONE ANDY RODDICK "I love you @serenawilliams It's been the pleasure of a lifetime to watch you become what you have. Can't wait to see what you do next. Thank you my old friend."

LOS ANGELES LAKERS BASKETBALL GREAT MAGIC JOHNSON "Congratulations, Serena for an inspiring career! Cookie and I are so excited for you. I remember when we talked about you becoming an entrepreneur. Now, I look forward to watching you grow in business!"

WORLD CUP-WINNING AMERICAN SOCCER PLAYER ALEX MORGAN "Serena fighting until the last point, always. You've given so much to tennis, and so much to women's sports. Thank you @serenawilliams."

WORLD CUP-WINNING GERMAN SOCCER PLAYER JEROME BOATENG "Massive respect on that amazing career. One of the greatest athletes in history. And far more beyond that. Thank you for everything @serenawilliams."

FORMER TENNIS WORLD NUMBER FOUR JAMES BLAKE "Serena. Thank you for being you and the inspiration to so many men and women. I've never seen a more intense competitor and it was an honour to share a court with you and watch history. Simply the best."

AMERICAN TALK SHOW HOST OPRAH WINFREY "25 years. Champion. Shero. Legend forever!"

SEVEN-TIMES TENNIS GRAND SLAM CHAMPION MATS WILANDER "Serena has meant so much for tennis and the world, but for America as well. I was watching the crowd and there are so many people here that have never been to a tennis match before... she has brought tennis to a completely new level and transcended the sport. We are going to remember Serena the person forever."

INDIAN CRICKET GREAT SACHIN TENDULKAR "Age is not what the body tells you, but what your mind tells the body. Teenagers can solve world's biggest problems, adults can pick up something new & excel. Sport inspires society to push limits & achieve the impossible. Congratulations on an inspiring career, @serenawilliams."

OLYMPIC TRACK CHAMPION ALLYSON FELIX "I'm so grateful for @serenawilliams. What she has given this sport and us will never be lost on me. #ThankYouSerena."

BASEBALL HALL OF FAMER DEREK JETER "It's been a joy watching greatness! Congrats Serena!"

FORMER TENNIS WORLD NUMBER SEVEN BARBARA SCHETT "It's hard to believe the Serena Williams era is finished, probably the Venus Williams era is finished as well. It was just unbelievable how she held up such a big fight at the end."

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