Flavia Pennetta of Italy kisses her Women's US Open Tennis champion trophy during a photo call at the Top of the Rock in New York, Sept 13, 2015. [Photo/Agencies]

Toast of the tennis world

Flavia Pennetta's first major title - and surprise retirement announcement - drew congratulations from around the tennis world.

Serena Williams, whose bid for the calendar grand slam ended on Friday with a stunning US Open semifinal loss to eventual runner-up Roberta Vinci, tweeted: "Congrats. I'm so happy you won. You deserved it. I am also happy for the rest of your life's journey. I will miss your smile."

Pennetta is the second Italian woman to win a major championship. The first, 2010 French Open winner Francesca Schiavone, tweeted: "Fla, welcome to the club."

Some other reactions from current and former players:

Caroline Wozniacki: "Wow!! @flavia_pennetta talking about finishing off in style!! Couldn't happen to a nicer person! Congratulation and happy retirement!!"

Madison Keys: "AND what a way to go out @flavia_pennetta!! Enjoy retirement."

Sabine Lisicki: "OMG Flavia did not just say that she finishes her career NOW!?!?? @flavia_pennetta #noooo."

Jimmy Connors: "No better time to retire-on top and a Champion!! Well done!!!!!"

Andy Roddick: "Wow! How cool was that? Talk about walking off in style ...."