Tennis legend Martina Navratilova has popped the question to her girlfriend Julia Lemigova on the big screen at the US Open.

The 57-year-old proposed in a TV suite off-court in between the men’s semi-finals to the cheers of fans who watched on live.

"I was very nervous. It came off, and she said yes,” she told the Associated Press.

“It was kind of an out-of-body experience.

“You’ve seen people propose at sporting events before, in movies, in real life, and here it was happening to me.

“It was cool.”

The 57-year-old proposed in a TV suite off-court in between the men’s semi-finals to the cheers of fans who watched on live. (AAP)

The pair have been together for six years and hope to get married in Florida, where they live.

While not yet legal, a judge recently ruled that the state’s ban on gay marriage is unconstitutional.

The couple said they expect the laws to change within a year.