OU (11-9, 3-3 in Big 12 Conference play) led by as many as 15 points in the first half and was up 38-30 at halftime.
Freshman Cameron Clark (11 points) was the only Sooner beside Pledger to score in double figures. Iowa State was led by freshman Melvin Ejim, who scored a career-high 19 points off the bench.
"We really only had one guy scoring for us and that was Steve," Capel said. "Cade (Davis) and Andrew (Fitzgerald) uncharacteristically were struggling offensively ... But I'm really proud of our guys. Once we got it into overtime we felt really good."
The Sooners opened the game red hot, hitting 13 of their first 17 shots but were dominated on the boards (43-29), which helped ISU own a commanding lead in second-chance points.
"We've got to rebound better," Capel said. "I thought the first half we executed our game plan almost to perfection. In the second half we didn't do as good a job with our transition defense and keeping guys out of the paint ... But this was a good win, our first road win since at Utah in 2009."