WASHINGTON (Reuters) - President Barack Obama, a big basketball fan, tweeted his congratulations to the University of Dayton for its "huge upset win" over Syracuse University in the second round of the NCAA men's basketball college championship on Saturday.

Dayton, a No. 11 seed in the South region, defeated No. 3 seed Syracuse 55-53. Dayton won a surprise victory over No. 6 seed Ohio State in the first round.

"Devin Oliver, I may need to take you up on that pick-up game one of these days," the president said in a Twitter post signed "bo," which means he wrote it himself. Oliver, a 6-foot, 7-inch (2-meter) senior forward for Dayton, was ESPN's player of the game with 10 rebounds and 7 points.

Obama played high school basketball and continues to play recreationally. He had forecast Dayton would lose in the first round.

The president is known to unwind by watching sports on television and reporters could see basketball games on the screen in the front cabin of the president's plane during a flight to Florida on Thursday, the first day of the tournament.

The president leaves for Europe and the Middle East on Sunday with the crisis in Ukraine a pressing global problem. Not everyone on Twitter shared Obama's enthusiasm for basketball.

"You have bigger issues to be worrying about," one person tweeted in response.

The national championship game is April 7.

(Reporting by Mark Felsenthal; Editing by Lisa Shumaker)