Lewis converted 6 of 10 3-pointers and the Longhorns (5-2) won their third straight game.
Jordan Reves led Texas-Arlington (3-2) with 15 points but the Mavericks posted their lowest score of the season. UT-Arlington has never beaten Texas in eight attempts.
Texas led 3-2 after a 3-pointer by Lewis about three minutes into the game and never trailed after that.
The Longhorns used 13 3-pointers -- eight in the first half -- to distance themselves from Texas-Arlington and finished shooting 50 percent from beyond the arc.
Texas was 23 of 51 shooting from the floor against the nation's top field-goal percentage defense. The Mavericks had not given up more than 63 points to an opponent this season. Texas surpassed that mark with 7:54 remaining on a pair of free throws by Javan Felix.
Nike Men's Texas Longhorns White Hyperelite ELITE Basketball Game JacketShop
Should the 76ers take Ben Simmons No. 1? What if they get the Lakers' pick, too? And how does the rest of the top 10 shake out? Our Insiders run their latest mock draft, with Philly on the clock.
ESPN college basketball reporter Andy Katz discusses the need for the Pac-12 putting in place rules on that would prohibit storming the court after a win.
Yes, the Class of 2016 saw Kentucky and Duke finish on top. It wasn't without its twists and turns, though. So what were the most notable surprises?