Kelly Olynyk, Gary Bell Jr., Kevin Pangos and Przemek Karnowski each had eight points for Gonzaga (5-0).
The Zags outrebounded Oklahoma, 51-24.
“That was a really, really good win for us,” Gonzaga coach Mark Few said. “We played really good. Got back to playing our style. We attacked on the offense end all night, and did another great job playing defense.”
Oklahoma (3-1) got 13 points from Romero Osby. Isaiah Cousins had 10 points.
“Gonzaga did a terrific job in dictating pretty much in every way,” Sooners coach Lon Kruger said. “Anytime you get whipped that badly on the boards, you know they were a lot more physical, a lot more aggressive to loose balls. It’s a terrific learning opportunity for us, and we’ve got to get that from it.
“Otherwise it’s a waste of time. So we’ve got to learn from it.”
Gonzaga will play Davidson, which beat West Virginia 63-60, in Sunday night’s championship game.
The Wildcats and Zags have some recent history.
The Wildcats, then a No. 10 seed, beat No. 7 seed Gonzaga, 82-76, in the first round of the 2008 NCAA tournament.
Gonzaga beat Davidson, 103-91, in the Battle in Seattle at KeyArena in 2009.
Oklahoma will close out the tourney Sunday against West Virginia.
Consecutive jumpers by Bell and Harris, who also slammed in a rebound, gave Gonzaga a 43-25 lead three minutes into the second half. Harris had 14 of his points during the second half.
“I think it was just the game coming to me at that point,” Harris said. “I played more aggressive. That was really the main key.”
Pangos’ 3-pointer extended the Zags’ lead to 53-31 with 12 minutes to play.
Olynyk had an in-close basket and David Stockton, son of former Zags and NBA star John Stockton, scored on a layup as Gonzaga built a 59-34 lead midway through the second half.
Gonzaga got points from nine players — led by Bell, a Kentridge High graduate, with five — en route to a 32-22 halftime advantage.
“That’s one of the strengths of our team this year is depth,” Pangos said. “That’s a big thing with our team because we just wear down other teams.”
Stockton’s fastbreak layup in the final minute of the half gave Gonzaga a 32-21 lead.
Olynyk had a dunk and layup as Gonzaga went ahead 14-5 just over eight minutes into the game.
Oklahoma trailed 14-8 despite going 2-for-15 from the field during the opening 101/2 minutes of play.
“You could say, well, we just missed shots, but Gonzaga had something to do with that,” Kruger said.
Steven Pledger’s jumper cut the Sooners’ deficit to 18-13 with eight minutes to go in the half. Andrew Fitzgerald had a slam that got Oklahoma to 20-17 two minutes later.