(CNN) Keith Thurman vowed to end Manny Pacquiao's career but it was the Filipino boxing legend who taught his younger rival a lesson in Las Vegas.

The 40-year-old set the tone by flooring Thurman in the first round with a straight right hand and won the 12-round bout on a split decision to become the oldest welterweight champion in history.

Pacquiao seemed to have the clear advantage Saturday but one ringside judge, Glenn Feldman, gave the 30-year-old American a 114-113 advantage.

Dave Moretti and Tim Cheatham, though, both scored it 115-112 to Pacquiao.

Manny Pacquiao beat Keith Thurman in the WBA welterweight title fight Saturday, flooring the American in the first round.

Thurman lost for the first time (29-1) while Pacquiao collected a 62nd victory (62-7-2) and said it wouldn't be his last fight, either.

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