"Very surprised," was the verdict of fellow Wimbledon winner and compatriot Amelie Mauresmo, skipper of the French Fed Cup team, and who in recent months had assumed some coaching duties with Bartoli.
Mauresmo said she had not seen the decision coming but that the pair had been in contact overnight, first by text message, then by telephone.
"I am very surprised by this announcement. I had not seen any particular sign it was in the offing. I just have to take it on board and wish her all the best in her new life," Mauresmo told a news conference organised by the French Tennis Federation after Bartoli dropped her bombshell overnight in Cincinnati.
"Of course there were one or two physical things and it's true that in general these things don't get better as you get older.
Clearly it was too much for her," Mauresmo, the 2006 Wimbledon and Australian Open champion, said in allusion to Bartoli's confession that the game had been taking too much out of her in recent months as she finally captured her first Grand Slam singles crown at the 47th attempt.
Others from the tennis world also expressed regret at Bartoli's decision, including former Wimbledon winner and number one Lindsay Davenport, another US great Pam Shriver, French former Davis and Fed Cup skipper Guy Forget and Croatian former men's Wimbledon champion Goran Ivanisevic.
"Hope she continues to enjoy what she has accomplished. I wish her all the best," tweeted Davenport.
Czech Petra Kvitova and American Mardy Fish took to Twitter to say they were saddened by the news, drawing a grateful response from Bartoli herself on the social networking site.
"So sad to hear that Marion Bartoli is retiring -- Has been a pleasure to know you, my fellow Wimby champ," Kvitova said.
Responded Bartoli: "Thanks Petra,it was my pleasure too!!! But I will still come and see you on tournaments haha you were so nice all the time."
Fish, who has struggled with injuries throughout his career and is now battling to regain his confidence after a heart scare, wished Bartoli luck.
"Sad to see Marion Bartoli retire yesterday," he tweeted. "She is a sweetheart. I was always a fan."
"Hey to all of u! 4:55 am can't sleep of course, reading all your sweet messages, and it makes me cry, thank u for sending me all this love," Bartoli tweeted.
Shriver, a five-time Wimbledon doubles champion, also tweeted best wishes.
"If I had ever won Wimbledon singles I would have retired ASAP. She always did things in her own style!!! Marion go live happily ever after," Shriver wrote.
Forget said he worried the decision might have been made in haste following a bad defeat in the second round at Cincinnati to Romania's Simona Halep.
"Marion is a very smart girl, she is so dedicated about the sport that I'm always very cautious about someone's quotes right after a defeat, and that happened right after she lost. I hope she is going to change her mind. You don't want to have regrets looking back," said Forget.
"Being a professional player is such an exceptional job and you don't want to look back in a few months or years later and think "why did I stop?'
"Don't rush it, just don't rush it. Take time, go to the beach for a few days, go running in the park, just get your head together, spend some time with your friends... don't take such a radical decision only a few weeks after winning the biggest tournament in the world," Forget said from the ATP Champions Tour at Knokke, Belgium.
Ivanisevic, Wimbledon champion in 2001 for his only Grand Slam, said from the same event: "What she did at Wimbledon was fantastic, but she will regret this decision when Wimbledon comes (next year).
"There is nothing like playing at Wimbledon as "Wimbledon champion". I couldn't defend, I was injured," reflected the Croatian, who had to cry off a title defence in 2002 before a 2004 swansong.
WTA CEO Stacey Allaster paid tribute to Bartoli.
"She is an inspirational champion and a great ambassador for women's tennis who has dedicated her life to the sport and (has) given so much back to the game," Allaster said.
"I am so proud of her for who she is, her values and for fighting to realise her dream of winning Wimbledon."