The Illini (3-0) led by eight at halftime. But the Crusaders (2-1) clawed back to within two at 49-47 with an 8-0 run capped by a 3-pointer by Bobby Capobianco with 6:43 to play.
Then Illinois guards Tracy Abrams and Rayvonte Rice scored on back-to-back drives into the paint on the much bigger Crusaders to give the Illini a 54-47 lead, part of an 11-1 run that stood up.
After Capobianco's shot the cold-shooting Crusaders scored just that single point over the next five-plus minutes.
Both teams spent the night missing far more than they made, some of it the result of tough defense and some of just cold shooting. Illinois hit 31.8 percent of its shots and Valparaiso 32.7.
At least five of the Crusaders misses were air balls. Illinois opened the second half playing fast, running at the bigger Crusaders. But over the first six and a half minutes, all that pace did was turn an eight-point halftime lead into a nine-point edge at 45-36.
Then the Crusaders started climbing back.
Alex Peters' layup in traffic on the baseline made it 47-39 with 9:06 to play, and the game felt closer than that.
The Crusaders outscored the Illini 8-2 over the next two and a half minutes before Abrams and Rice took control for Illinois. Joseph Bertrand added 14 for the Illini and Abrams had 12. Jon Ekey had a game-high 15 rebounds for Illinois. Center Nnanna Egwu had 10 points before fouling out late.
Jordan Coleman led Valparaiso with 15 points and Lavonte Dority played through an early ankle sprain to add 12 points, including a pair of 3-pointers.
Illini coach John Groce said this week that Valparaiso's size would test Illinois. The Crusaders have four players who are 6-10 or taller, including 7-0 center Moussa Gueye, and guard-heavy Illinois has just two.
But the Illini outrebounded the Crusaders 49-36, and held them to nine offensive rebounds, most of them late in the game, and just four second-chance points.
Gueye had just two rebounds and didn't score a point.
Ekey ended a sometimes ugly, physical first half with a rainbow of a 3-pointer at the buzzer to give the Illini a 33-25 lead.
Points were looking unlikely on the possession. Abrams fed Ekey with an inbounds pass with just two seconds left on the clock. But the 6-7 forward spun quickly and fired the fade-away. Just a minute earlier, Valparaiso had closed to within three at 28-25 on a pair of free throws by Coleman.