When the Atlanta Falcons appeared headed for a runaway victory in Houston on Sunday, Canadian tennis player Bouchard tweeted to her one million followers: "I knew Atlanta would win btw."
That prompted a follower to ask her if she would go on a date if the New England Patriots pulled off a comeback victory.
Bouchard agreed, and was left to regret it after the Patriots defied the odds to win in overtime.
"Lesson learned. Never bet against (Patriots quarterback) Tom Brady," she tweeted.
On Monday, Bouchard said she would "stay true to my word" and go on the date with her fan, who says he is from Chicago and is studying in Missouri.
Bouchard, 22, was a rising star in 2014 when she reached the Wimbledon final, but has slipped to 45th in the latest women's rankings.