The Sooners (4-5) had lost five in a row away from the Lloyd Noble Center but were able to stay perfect at home this season by answering the Bulldogs' 3-point flurry with one of their own.
Gardner-Webb (6-6) cut a 19-point deficit to four by making five of its first six 3-pointers in the second half.
Jon Moore led Gardner-Webb with 14 points, and Luke Davis scored 10.
Cade Davis scored 15 and Clark, a freshman, had a career-high 13 points for the Sooners.
Stefon Johnson hit a buzzer-beating 3 to cut the Bulldogs' deficit to 34-18 at halftime, and four different players combined to go 5-for-6 from 3-point range to start the second half for Gardner-Webb.
Luke Engelken, Luke Davis and Brian McNair connected during a 9-0 spurt that whittled the deficit to 41-37 with 13:12 to play. That prompted Sooners coach Jeff Capel to call time out and put Fitzgerald back in the game despite three fouls.
Fitzgerald immediately spun past Santoine Butler and converted a three-point play, and Cade Davis restored the lead to double digits with a 3-pointer.
After getting back within striking distance, Gardner-Webb -- picked to finish last in the Big South Conference -- had just one basket over the next 5 minutes. When Clark hit the last of the Sooners' three straight 3-pointers, it pushed the lead to 63-47 with 4:38 remaining.
The Bulldogs fell behind early by missing nine of their first 10 shots and didn't make their second basket until more than 10 minutes had elapsed.
The Sooners pulled away with a 17-3 run highlighted by Clark's two-handed jam off an alley-oop from midcourt by Blair. Clark also had two steals in Oklahoma's aggressive zone defense, and he and Pledger combined to hit six straight free throws to push the lead to 31-12 with 2:29 left in the first half.
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Maryland point guard Melo Trimble, considered a lock to leave the program before struggling in the second half last season, has withdrawn from the NBA draft and will return for his junior season.
Louisville's Chinanu Onuaku, who recently underwent a medical procedure to correct a heart rhythm issue detected during the combine, will keep his name in the NBA draft pool.
Andrew White III will return to the Nebraska men's basketball team next season after removing his name from the NBA draft.