SAN FRANCISCO (CBS SF) — Tennis champion Serena Williams shocked a couple of neighborhood tennis players at San Francisco’s Dolores Park this weekend by strolling up and challenging them to a match.

Williams, ranked the No. 1 player in the world by the Women’s Tennis Association, happened to be walking by Dolores Park with a little dog when she decided to hit around with two men who had just finished up a match.

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The impromptu tennis challenge – captured on video and posted to Snapchat – shows Williams at first just watching the men’s match from outside the courts. Williams then wonders out loud whether she should ask them to play and eventually decides she would play.

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Williams, wearing streets clothes and boots, approached the two men who appeared to be completely shocked. They offered her a racket, and Williams put down the little dog she was holding, tightened her boots and took to the court.

Williams, who some consider the greatest female tennis player of all time, recently got engaged to San Francisco-based Reddit co-founder Alexis Ohanian.

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By Hannah Albarazi – Follow her on Twitter: @hannahalbarazi.