'Proud' Michelle Obama congratulates Serena over successful 2015 season

First Lady Michelle Obama is proud of Serena Williams even as she lost in the US Open women's semi-final on Friday.

- Serena finally falls after riding her luck

The American President's wife took to Twitter to share her feeling after Serena suffered a devastating loss of her career, saying "So proud of you, @SerenaWilliams. What you did this year was amazing. -mo #USOpen2015.”

Italian Roberta Vinci crushed the world number one's hope of completing a calendar grand slam by reaching the women's singles US Open final for the first time in her career.

The unseeded Italian produced a resilient performance as she fought back to overcome the 21-time Grand Slam champion 2-6, 6-4, 6-4 in a pulsating semi-final clash at Flushing Meadows.

American tennis star Serena was hoping to secure the first calendar grand slam since Steffi Graff in 1988. 

Image: Serena Williams of the United States

Photograph: Matthew Stockman/Getty Images