INDIANAPOLIS — After one of those occasional matchups that comes too soon in a bracket and feels like a glitch and sends away some gem of a team, the NCAA men’s basketball tournament waved goodbye to a fantastic and alluring No. 1 seed Illinois on Sunday. At the same time, it held on to something else fantastic and alluring.

Loyola Chicago, that team from the smaller Illinois school and the so-called smaller conference, deprogrammed Illinois, 71-58, with a performance that looked 0 percent like the emotion of an underdog and 100 percent like the know-how of a colossus. It gave the Ramblers a win that might just come up in conversation a time or two up along Lake Michigan across the next century or so.

To ease the horror of the wind blowing off said lake, they might tell of how this showcase second-round game in the Indiana Pacers’ home arena wound up with the score decisive and the seconds ticking away and the pandemic-scattered fans in maroon and gold chanting: “L-U-C! L-U-C!” Their team had caused them not even an iota of anxiety, barging ahead early and staying ahead always, leading 33-19 early and then never less than 39-33 afterward, leaving the wealthier downstate brother looking like something other than itself, occasionally confused and completely defused.

“We just stuck to the game plan, really,” said Cameron Krutwig, a senior co-leader with a glowing stat line. “No one was doing anything out of their body, out of their mind.”

Illinois Coach Brad Underwood, whose program had legitimate dreams of much bigger things, said: “The first 10 minutes of the game, they got us on our heels, and we never really recovered. We had stretches. But they just rocked us.”

Loyola Chicago Coach Porter Moser said, “The guys believed,” stressing a “confident respect” for Illinois and saying, “It’s amazing what happens when you get a group of guys who believe.”

Given the look of their mastery and Moser’s mastery drawing up their mastery, it’s hard to imagine how they couldn’t have believed.

Those sages Krutwig and Lucas Williamson, after all, have played in the hubbub of a Final Four, in 2018, and they and their mates knew enough to present Illinois with a defensive puzzle it could not solve as its season died at 24-7. Krutwig, the 6-foot-9, 255-pound bale of versatility from the northwest Chicago suburb of Algonquin, spent the day ramming commendably with 7-foot, 285-pound Kofi Cockburn — “He’s like a brick wall,” Krutwig said — and piling up some luscious stats.

See them, love them: 19 points, 12 rebounds, five assists and four steals. He used what Moser calls his “mental motor” that keeps him perpetually “ahead of the play.” He got help from smart satellites around him such as Williamson and an impressive Marquise Kennedy, each with 14 points, and they’ll all go together to a place Krutwig has been: the Sweet 16, opposite Oregon State in the Midwest Region.

“Man, Marquise Kennedy, another Chicago guy, he was so big tonight,” Moser said, soon adding, “We had contributions all over the map.”

Clearly under-seeded at No. 8, Loyola Chicago (26-4) craftily took a 33-19 lead with just 76 seconds left before halftime, the stat sheet filled with the kinds of numbers that might suggest a seething over a smaller reputation (and seeding): seven steals to one, four turnovers to nine, 11 assists to seven.

Still, it all looked like a titan’s precision more than an underdog’s inspiration.

The Loyola Chicago defense, which killed joy all season at the rate of a nation-best 55.7 points per game for others, bothered the Illini into clear discomfort that shouted their 81.3 points per game weren’t coming this day. They squeezed Chicagoan star Ayo Dosunmu into extremely limited beauty, such that his high-level basketball smarts saw fit to take only 10 shots, four of which he made toward nine points with six turnovers. They crowded Cockburn with too much company to enjoy, sometimes sending a third antagonist to the post to poke away the ball from a distracted giant, so that his 21 points and nine rebounds looked both like an achievement and an afterthought. And the Ramblers gave yet another hint that the coach who took them to the 2018 Final Four, Moser, knows better than most how to send an opposing offense spiraling toward a pity party.

“They made it very tough for us to run stuff,” Underwood said.

Krutwig said without resentment: “I guess people kind of forgot or something, but we were the number one defense in the country this year. I guess people kind of chalked it up to being a mid-major or something.”

Underwood added, “They did a really good job in their ball-screen coverage.”

At times, the Illini offense looked baffled as to how to proceed. All game long, the tournament champions of the season-long top conference tried the grueling art of chasing, subjecting their own scattered throng to fresh stomach knots. Once the score reached 59-46 at the five-minute mark, just after a beautiful Williamson drive and three-point play and just before an alley-oop from Keith Clemons got a nifty, tap-in finish from Krutwig, the whole thing looked unmistakably settled.

Afterward the Ramblers left the floor, but then they returned by Moser’s instruction — “Get out there and enjoy it!” — and they exulted and exulted for a very good while. One gem of a team was gone, and yet again it wasn’t the Ramblers.