Ishe Smith beat Cornelius Bundrage by split decision on Saturday night to claim the IBF 154-pound title.
Smith (25-5) won his first world title at 34, patiently counterpunching the champion through 12 sometimes dull rounds. The veteran managed by Floyd Mayweather Jr. wept with joy after becoming the first Las Vegas-born fighter to win a major belt.
Bundrage (32-5) was more aggressive in the early rounds, but tired. Smith staggered and cut Bundrage in the ninth while largely controlling the final four rounds to earn a comfortable victory.
Two judges favored Smith 116-111, while Bundrage won 114-113 on the third card.
Bundrage congratulated Smith on the victory, saying he had wandered away from his game plan. Bundrage had been the IBF champion since August 2010, defending the belt twice.