The Crimson Tide shot just 33.3 percent (9 of 27) in the first half, but Arkansas was worse — connecting on just 9 of 33 shots (27.3 percent).
Portis had eight of the nine first-half field goals for the Razorbacks, and his six blocks topped his previous best of three.
"We needed him," Arkansas senior Mardracus Wade said. "He stepped up big for us, just like we always thought he could ... I'm not surprised at all by what he did today."