"Playing in Dallas was an advantage," Oklahoma coach Kelvin Sampson said. "Anybody that advances to the Sweet 16 is good, but our fans helped us."
The game was tied at 49-49 with 11 1/2 minutes left when McGhee hit a pair of jumpers and two free throws to highlight a decisive 9-0 run.
After Romain Sato connected on a three-pointer and Alvin Brown hit one of two free throws for Xavier, McGhee converted a pair of free throws, Jabahri Brown hit a layup and Ere had a pair of free throws to open a 64-53 lead with 5 1/2 minutes left.
Xavier (26-6) pulled no closer than nine the rest of the way.
Oklahoma (29-4) converted 24 of 28 free throws, including 14 of 16 in the second half, and committed just six turnovers.
"We didn't get beat by a good team. We got beat by a great team," Xavier coach Thad Matta said. "They were clicking on all cylinders at all the right times, right out of the gate and right at the end."
The Sooners will meet third-seeded Arizona in the West Region semifinals Thursday at San Jose.
Oklahoma became the fourth Big 12 Conference team to advance to the Sweet 16, joining Kansas, Missouri and Texas.
"I think it was important for the league this year," Sampson said. "It was time because you have to win in March."
Sato scored 18 of his 28 points in the first half for Xavier.
"We play the same way they do," Sato said. "We were able to make some shots, but in the end we couldn't make the key shots."
David West, the Musketeers' All-American power forward, was matched up against McGhee and had 18 points and eight rebounds.
"I take every game as a personal challenge," McGhee said of his matchup with West. "I guess since our team won the game, I was the better player in the game."
McGhee scored 10 points on a three-pointer, a three-point play and a pair of baskets in the first 6 1/2 minutes as Oklahoma built a 19-10 lead.
"I felt like I defended him (McGhee) well, but it is hard to defend a guy who starts off the game making five or six field goals in the first three minutes of the game," West said. "I let him get going too early in the game."