Ejim had two 3-pointers and six dunks during his big game, one on a spectacular fast-break lob from DeAndre Kane that gave the Cyclones (18-4, 6-4 Big 12) a 67-52 lead and effectively put the game out of reach.
A 6-foot-6 senior, Ejim scored 20 straight Iowa State points during one stretch in the second half. It was his 30th career double-double.
Georges Niang added 11 points and Kane finished with 10 assists for the Cyclones, who avoided a letdown after their thrilling three-overtime victory at Oklahoma State on Monday, their first win in Stillwater since 1988.
Kyan Anderson led the Horned Frogs (9-13, 0-10) with 27 points and eight assists. Amric Fields scored 18 points and Karviar Shepherd had 11 for TCU, which was coming off single-digit losses to Texas Tech and No. 15 Texas, but could not keep up with the Cyclones and the high-flying Ejim.
Ejim padded his Big 12 scoring lead with a performance that topped the previous conference record of 44 points by Kansas State's Denis Clemente in 2009 and the Wildcats' Michael Beasley in 2008. His previous high had been 23 points against Oklahoma last season.
Iowa State's school record is 54 by Lafester Rhodes in an overtime victory over Iowa in 1987.
Ejim stayed in the game until 19.9 seconds remained, when he left to a lengthy standing ovation.
The game was expected to offer a break for the Cyclones after they played four straight against Top 25 teams and eight in a row against teams that were ranked at one time or another. But the Horned Frogs proved to be a little more stubborn than anticipated despite a horrible start.
TCU gave up the ball on a shot clock violation on the game's first possession, Dustin Hogue followed with a 3-pointer and Iowa State led from then on as the Horned Frogs missed nine of their first 10 shots.
Despite some sloppy play at times, the Cyclones built a 16-point lead late in the first half, then had the lead whittled to seven before Ejim went on his tear to wrap it up.
TCU shot 29.6 percent in the first half and did not have more baskets than turnovers until Anderson hit the second of two straight 3-pointers with 45 seconds left in the first half, cutting the lead to 32-22.