Madison Keys was looking forward to the opportunity to play on the same World Team Tennis team as childhood idol Venus Williams.

Monday, Keys got a bigger thrill, upsetting Serena Williams, Venus' sister and the freshly crowned Wimbledon champion, in a WTT singles match.

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Playing for the Philadelphia Freedoms, the 14-year-old Keys, who grew up in Milan, Ill., defeated Serena Williams, playing for the Washington Kastles, 5-1.

Keys improved to 2-1 in WTT singles play.