McIntosh was 7 of 9 from the field and hit all six of his free throws for Northwestern (8-4). Olah hit 5 of 10 shots, 6 of 10 free throws, grabbed seven rebounds and had three blocks.
D'Juan Miller led Illinois-Chicago (3-10) with 14 points and seven assists. Jake Wiegand had a game-high 10 rebounds, as the Flames dropped their third game in a row.
Illinois-Chicago was without top scorer Jay Harris, averaging 15.8 points per game. He was a game-time decision because of a strained ligament in his right knee, which he sustained in practice on Sunday.
The Flames pulled as close as 45-38 on Jason McClellan's 3-pointer with 6:45 left in the second half. But Olah responded with a pair of free throws and the lead wasn't seriously threatened the rest of the way.
McIntosh and Olah set the tone with 10 points each in the decisive first half.
"We started fast with a lot of energy," said McIntosh, who also had four assists.
The victory was the second for Northwestern since coach Chris Collins and his staff made changes to create a more upbeat atmosphere before games.
Prior to a win against Western Michigan, players formed a line and locked arms to stress team unity. Chairs also were removed from locker room to get the players on their feet and boost energy levels.
"I'm not one to just stand pat," Collins said. "I'll change lineups. I'll change what we're doing. We've changed our pre-game in terms of how much we say to the guys. We're trying to be more rah-rah versus locked into strategy just to get some life."
After Lance Whitaker gave Illinois-Chicago a 2-0 lead, McIntosh and Olah combined to score the next 16 points. The Wildcats held Illinois-Chicago scoreless for seven-plus minutes, which Ahman Fells finally stopped at the 12:16 mark.
"In these last two games, it was more like the defense our program is accustomed to seeing," said Collins, whose team blocked nine shots and forced 10 turnovers. "Sometimes you have to get exposed in order to embrace change, that's what that game (against Central Michigan) did for us."
The Wildcats connected on only 6 of 35 tries in first half and 15 of 60 overall, as their season-long struggles in the field continued.
"In the first half, when we were hitting some lulls, there were some shots that Jay probably would have been able to knock down for us," head coach Howard Moore said. "But we've had those lulls with him in the lineup, too."
Illinois-Chicago's leading scorer, Jay Harris, watched the game in a walking boot on the bench but could return to action later this week. One week earlier, the fifth-year guard was selected as the Horizon League Player of the Week on the heels of a career-high 32-point performance against Central Florida.
Northwestern's Alex Olah played with a lower back problem that was not believed to be serious. Reserve swingman Scott Lindsey was limited to eight minutes because of a twisted ankle and he sat out the second half.
Illinois-Chicago: The Flames had won four of the previous five matchups between the two clubs, including the last three at Welsh-Ryan Arena. Northwestern now holds a 5-4 all-time record against Illinois-Chicago.
Northwestern: It was the Wildcats' fourth game in a nine-day span. ... Two children (8th graders and under) were admitted free to Monday's matinee with one paid adult admission.
Illinois-Chicago: plays Bradley on Sunday.
Northwestern: hosts Northern Kentucky on Saturday.