Marcus Relphorde had 24 points to pace Colorado (9-6, 0-1), which had won three of four entering Saturday's game. Alec Burks and Cory Higgins finished with 21 and 15 points, respectively, for the Buffaloes.
In a close game early, Colorado got within 35-30 after two free throws from Dwight Thorne II with just under eight minutes left in the first half. But Texas followed with a 14-2 run to begin pulling away.
James made 1-of-2 from the line with three minutes left to cap the rally and make it a 49-32 contest, and the Longhorns were ahead 57-42 at the break.
Colorado began the second half with a three from Relphorde, who moments later had a three-point play to get the Buffs within 59-50. But Johnson followed with a jumper, and Texas continued to hold a lead just into double digits as the game went down the stretch.
After Trey Eckloff's layup got Colorado within 85-73 with about 8 1/2 minutes to play, Jordan Hamilton got a tip-in for Texas, which started a six-point burst. Johnson and Alexis Wangmene each had a pair of foul shots to boost the Longhorns' lead to 91-73 with just over six minutes left, putting the game out of reach for the Buffaloes.
Hamilton finished with 12 points...Fourteen of Texas' 15 wins this season have come by double-digits...The Longhorns have won six in a row in this series...Colorado shot 53.6 percent, while Texas made 55.2 percent of its shots.