The Sooners led just 33-25 at halftime, but that's when they turned it on.
Behind 16 forced turnovers after intermission, OU managed to score 26 points off TOs.
"It makes everything a little bit easier," said head coach Sherri Coale. "It's just like room to breathe when you do that. It was really mano-a-mano defense, just the guy on the ball being aggressive, being active and making them unsure about what they would do next."
They shot the 3 at a 66.7 percent clip, converting 6-of-9 for 18 points.v
And they shot it 72.2 percent from the field overall in the second half.
After trailing in the rebounding battle 31-22 at half, OU eventually won that 40-39.
About the only thing that didn't go right in the second half was free throws, where OU made just 9-of-16 after hitting all five in the first half.
So, it was an all-around show to say the least, as the Sooners managed to get to triple digits.
"We opened up the second half with giving up another offensive rebound and then, from that point forward, we only gave them two," Coale said. "Our attention to detail to the things that were giving us trouble in the first half were corrected. I really credit Whitney [Hand] for taking care of the locker room. I didn't have to do anything but tell them what to run in the second half because she really took care of everything that was wrong in the first half."
As Coale alluded to, it certainly didn't start off well.
OU didn't make a field goal for the first 4:37 of the contest until guard Morgan Hook successfully completed an and-one play to tie it up at 3-3.
"Wow, I think she's been really, really good," Coale said of her point guard. "Steady, making open shots, making good decisions, she's improving defensively, that was the biggest flaw of her game last year, still got to work on blocking out as all of us obviously. But I really couldn't be more pleased with her progress at this point."
The Sooners briefly trailed again, but that was the last time, as they used a 17-2 run to extend a comfortable double-digit lead midway through the first half.
But Grand Canyon didn't go away at that point and kept it close for an 8-point deficit after 20 minutes.
It was all over from there, however.
Guard Aaryn Ellenberg, who was on fire throughout the game and finished with 21 points on 8-for-16 shooting, put the Sooners up by double-digits for good when she hit a 3-pointer to make it 39-27 with 17:11 remaining.
OU led by 20 at the 13:30 mark, 30 by the 8:29 mark and 40 with 5:37 to go.
Another flurry, a 17-5 spurt, put the Sooners up 52 with 21 seconds left.
"I think that everybody knew what they were doing wrong," Hand said. "I think I had only taken three shots and I was thinking there were things that I had to fix. Rebounding obviously was awful. They responded really well, and I thought everybody came out really well in the second half.
Ellenberg and guard Sharane Campbell each led all scorers with 21, while guards DaShawn Harden, Hand and Morgan Hook had 17, 12 and 12, respectively, and center Nicole Griffin added 11.
Grand Canyon only had a pair of players in double figures, as guard Maylinn Smith finished with 12 and forward Stevie Kamp managed 11.
The Sooners open up the regular season at 2 p.m. Sunday against Sacramento State.