He also liked the result of Wednesday's game.
Guard Keith Appling added 11 for the Spartans (16-1, 5-0 Big Ten), who won their ninth straight overall and improved to 8-0 away from home and 4-0 on their opponent's home court despite setting a season low in points.
The Spartans were certainly challenged by Northwestern, something Izzo noted repeatedly during his postgame remarks.
"Give (Northwestern coach) Chris (Collins) credit. I think he's got guys that play hard," Izzo said. "That's the number one thing that will give him a lot of wins in his career."
The Spartans survived despite health issues.
They also had another injury scare with 47.6 seconds left in the first half when Appling appeared to strain his right arm. He stayed in the game, and helped Michigan State stretch its lead in the second half. Michigan State took its first double-digit advantage with 5:43 left on two Harris free throws.
An Appling injury would be about the last thing Izzo wanted to see.
"I don't know what he did. I was smart enough as a coach... I've got so many injuries but when he got injured... he's the toughest kid I've got, I didn't even ask him if he's OK," Izzo said. "I just said, 'You're playing.'"
Michigan State held Northwestern (8-10, 1-4) to just 28.3 percent shooting from the floor. That defense helped the Spartans survive a night when they made 2-of-16 3-pointers and were 20-of-52 overall.
"We still feel like there's some areas we can improve on," Appling said. "We've just got to get back to the drawing board and correct some of the mistakes we made tonight."
Northwestern, meanwhile, is trying to build its program.
Northwestern upset in-state rival Illinois 49-43 on Sunday, but was unable to knock off another ranked opponent Wednesday.
In conference play, the Wildcats have only cracked the 50-point barrier three times as they transition away from former coach Bill Carmody's Princeton-style offense. Izzo compared that to moving from a football wishbone offense to a pro-style attack.
Despite those offensive issues, Collins was proud of his players.
"I've told my team since the start of the year, really the only thing I ask of them is just to compete on every possession, put their hearts on the floor, and see what the results are," Collins said. "And whatever they are, we'll live with them. And I couldn't be prouder of how our guys played tonight."
Crawford, Northwestern's leading scorer, struggled from the field, hitting 1-of-8 shots. It continued a frustrating stretch for him, as he dropped to 17-of-53 in conference play.
"I've been struggling a little bit. I think defenses have done a good job of kind of keying in on me a little bit," Crawford said. "I've just got to do a better job. I can't turn over the ball and I've got to find myself better shots, so it's something I really need to improve to help my team out."
NOTES: Michigan State F Adreian Payne is averaging 16.2 points and 7.7 rebounds, and he is 18-for-41 (43.9 percent) on 3-pointers. The only two games the senior missed over his career were Saturday and Wednesday. ... Spartans coach Tom Izzo said after Saturday's game against Minnesota that "there's something bothering" F Branden Dawson. ... Chicago Bulls general manager Gar Forman was in attendance. ... Northwestern G Dave Sobolewski sat out his second game in a row after suffering a concussion in practice last week. In 16 games, Sobolewski is averaging 27.4 minutes and 6.7 points. ... Michigan State has won 18 of its previous 20 meetings with Northwestern. Under Izzo, the Spartans are 28-4 against the Wildcats. ... The teams play again Feb. 13 in East Lansing. They faced each other once in regular-season play the previous two seasons.