Dentmon entered for the jittery Venoy Overton in the game's first minute and then took over for the Huskies (13-11, 4-7 Pac-10), who had lost four in a row -- the past three at home.
Jon Brockman added 12 points and 17 rebounds for Washington, which won its fourth consecutive home game against the Bruins dating to 2004.
Josh Shipp scored 19 points, and Russell Westbrook had 18 for the Bruins (21-3, 9-2), who lost for the first time in six games and fell into a tie with Stanford atop the conference.
Washington's largest lead was nine, three times in the first nine minutes of the second half and again after consecutive baskets by Dentmon made it 65-56 with 2:14 remaining.
UCLA had chances down the stretch because of poor free-throw shooting from Washington.
But the Bruins couldn't take advantage.
NO. 13 XAVIER 76, SAINT JOSEPH'S 72
In Cincinnati, a matchup of the Atlantic 10's top two teams came down to the final minute. Lately, that's been Xavier's best minute.
Stanley Burrell scored 16 points and made a pair of clinching free throws with 13 seconds left, helping the Musketeers hold on for a win over Saint Joseph's.
Xavier (20-4, 8-1) solidified its hold on first place with its 12th victory in the past 13 games. This one wasn't easy -- the Musketeers blew a 14-point lead and had to rally in the closing minutes.
They scored the last eight points to pull it off.
NO. 14 INDIANA 59, OHIO STATE 53
In Columbus, Ohio, D.J. White and Eric Gordon finally got Indiana a signature win.
White scored 21 points and had 13 rebounds, and Gordon hit a number of big shots to lead the Hoosiers past Ohio State.
It was the first red-letter win for the Hoosiers (20-3, 9-1 Big Ten) against a team higher than No. 49 in the RPI ratings. The Buckeyes (16-8, 7-4) came in at No. 32.
Gordon finished with 15 points, hitting four free throws in the final minute.