'Holy crap!' Serena Williams surprises players on public tennis court

File- Tennis player Serena Williams speaks to CNN's Rachel Nichols after her sixth U.S. Open women's singles tennis title Sunday, September 7, 2014.

(CNN) -- Many tennis fans might wonder how they would fare playing against the world's best.

Yet few expect to be challenged during a friendly match on a public court.

That's exactly what happened in San Francisco on Sunday when 23-time time grand slam champion Serena Williams asked two unsuspecting recreational tennis players if she could share a court with them.

The exchange was captured and published on Williams' Snapchat account.

"Just having a stroll at night and I'm thinking about asking these guys if I can hit with them just to see their reaction," the world No. 1 can be heard saying as she approaches the court.

Understandably, the reaction was one of shock.

"Holy crap," one of the men can be heard saying.

Williams was welcomed onto the court but, because she didn't have tennis shoes with her, ended up playing in a pair of knee-high boots.

The moral of the story? "You never know when I could be coming to a tennis court near you," Williams said.

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