LAS VEGAS — Floyd Mayweather Jr. surrendered in a courtroom Friday to begin a three-month jail sentence for attacking his ex-girlfriend in September 2010 while two of their children watched.

Las Vegas Justice of the Peace Melissa Saragosa credited the undefeated five-division champion with attending weekly domestic violence counseling sessions — including one the day of the May 5 fight she allowed him to make — and with beginning to meet community service requirements she imposed in December. The judge then watched as Mayweather was handcuffed and taken away.

Mayweather didn’t say a word.

“He’ll be all right,” Mayweather’s friend, rapper 50 Cent, told reporters after arriving with Mayweather and speaking afterward with ring adviser Leonard Ellerbe outside the courthouse in downtown Las Vegas.

“It’s an uncomfortable situation for everyone,” he said.