The 32-year-old tennis star entertained an audience with a rendition of a Marilyn Monroe song "Diamond's are a Girl's Best Friend" in an Open Mic event in New York Wednesday night.

Instead of a tennis racket, World No. 1 Serena Williams was holding a microphone in a karaoke event at Arena Club in New York City that amused a number of people.

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Before taking stage at the Delta Airlines event, Williams was quoted saying "I'm really nervous."

Karaoke is Williams' "favorite thing" and likes to sing 80's and 90's rock because it's good for her voice. She also says that the trick about karaoke is picking songs that work for your voice.

"That way if you sing like a cat - like I do - you can still sound pretty good," Williams said.

The song made famous by Monroe in the 1953 film "Gentlemen Prefer Blondes" was actually not sung by her alone. She needed help in the phrases "These rocks don't lose their shape, diamonds are a girls' best friend" which was dubbed by famed soprano Marni Nixon.

But Williams didn't need help in singing those phrases for she actually sang it quite well while dancing on stage in a mini dress.

Williams is set to defend her U.S. Open title starting Aug. 25 at Flushing Meadows.

The 17-time Grand Slam champion did not win any Grand Slam tournaments so far this year. In fact, she didn't even reach the quarter-finals.

Williams did however win two Masters event, the Bank of the West Classics in Stanford and the recent Western and Southern Open in Cincinnati.

"This is definitely a level that can take me to the (U.S. Open) title. I still have a lot of work to do. It's definitely a better level than I've played all year, to be honest," said Williams, after winning the Cincinnati Masters.

Tagsserena williams, Marilyn Monroe, Marni Nixon