The Cowboys, who fell out of the top-25 on Monday, are now 16-8 overall and 4-7 in the Big 12, while the Longhorns improve to 19-5 and 8-3.
Smart's presence was missed, especially considering what he contributed (24 points, 11 rebounds, 6 steals, 5 assists and a blocked shot) in OSU's 87-74 victory over the Longhorns on Jan. 8 at Gallagher-Iba Arena in Stillwater.
The Cowboys led 3-2 early thanks to Markel Brown's three-pointer but the Longhorns scored seven points in a row to take the lead, and head coach Rick Barnes' team finished off a 19-6 run to take a 21-9 lead before Travis Ford called a timeout with 12:26 on the clock.
The Longhorns entered the game as the worst three-point shooting team in the conference but they made eight three-pointers in the first half and stretched their lead to as many as 26 points before going to the locker room at halftime with a 54-33 lead.
"Some teams have done some things that are uncharacteristic (against us) but we've got to look at ourselves," OSU head coach Travis Ford said. "We can't just say that they're hot. Like I told our team, there's a point where they're making some shots but we've got to do something about it. We just can't sit back and hope a team misses. You've got to defend well enough that you make them miss, and to start out the game we didn't do that."
The Cowboys, sparked by walk-ons Christian Sager and Mason Cox, went on a 15-5 run early in the second half to pull within 19 points but by that time the outcome had been decided. Sager hit back-to-back three-pointers during the run, and finished with a career-high seven points.
Cox, playing for the first time since the TCU game on Jan. 15, gave the team a much needed burst of energy in the second half. The 6-10 senior walk-on had played just six minutes and had not scored a point in OSU's first 23 games but he finished with two points, three rebounds, two steals and a blocked shot while playing six minutes against the Longhorns.
"The second half I thought we showed a little bit of heart, we played harder," Ford said. "I thought Mason Cox got in there and gave us some great minutes. What I loved about it when he got in there is that even our guys who were on the bench that I had taken out (of the game), they were cheering for him.
"That's a step in the right direction. That is not something that we've had. That is not something that we have seen. We've had guys coming out pouting because they're not in there, and for us to get this thing turned around we need plays from Mason Cox but we need other players who may have been playing a lot of minutes but maybe are not playing as well or somebody else is playing, we need them cheering their teammates on. We saw that tonight. We saw some guys cheering their teammates on, and we haven't had that.
"I liked that we played hard in the second half and made some plays. Give Texas credit, they came out and made shots tonight."
Le'Bryan Nash led the Cowboys with 23 points on 9-of-17 shooting from the field, but the rest of his teammates combined to make just 12 of 42 shots, and OSU shot just 35.6 percent for the game (their worst shooting game of the season).
Brown (18 points) and Kamari Murphy (10 points and 10 rebounds for the first double-double of his career) were the only other Cowboys in double figures.
Javan Felix, who entered the game averaging 11.8 points, scored 27 points to lead four Longhorns in double figures. Isaiah Taylor (16), Cameron Ridley (12) and Martez Walker (12) also were in double digits.
OSU will return home to Gallagher-Iba Arena to face Bedlam rival Oklahoma on Saturday afternoon.