INDIANAPOLIS — Kelvin Sampson keeps every practice plan he has ever created — from 1981, when he began his head coaching career at Montana Tech, to this year, his 11th at Houston — in a filing cabinet in his office.

During Sampson’s seven years out of college basketball as an assistant coach in the NBA, he filled new folders with others’ ideas and plays. One of his favorites was a baseline-out-of-bounds play that former Milwaukee Bucks coach Scott Skiles used to run for point guard Luke Ridnour in late-clock situations. He called it “51”. Sampson started running it himself when he coached NBA Summer League. He brought it to the Houston Rockets and ran it for James Harden. And every June since 2014, when Sampson returned from the NBA to revitalize Houston’s basketball program, it’s the first out-of-bounds play he teaches his Cougars.

On Friday night, game tied, 2.8 seconds left, Houston ball, Sampson huddled with his staff and debated what to call. What made sense was some kind of lob at the rim, because Purdue had a small lineup on the floor and no one would be able to jump with Houston center Joseph Tugler.

Sampson’s first thought: a play called Virginia Tech — which he says he calls VT for short “because I like vodka tonics.”

Nah. Too obvious.

“We’re going to run something we’re really good at executing,” Sampson told his staff.

But with a wrinkle.

The original 51 was designed to get Ridnour — played in Houston’s case by leading scorer LJ Cryer — running from the ball-side elbow to the opposite corner off a screen set by the center for a quick catch-and-release jumper.

Sampson knew the Boilermakers would be ready for that option, and he’d seen exactly how Purdue would guard it almost six minutes earlier when Cryer ran to the corner on another baseline out of bounds play. Boilermakers point guard Braden Smith, who was guarding the inbounder, jumped out to deny Cryer.

This time, Sampson told Cryer to run as far into the corner as he could, ideally pulling Smith out of the equation and opening up the lane line, where Tugler could slip right to the basket.

“It was unfolding in real time for me because I was watching the numbers,” Sampson said. “Two-on-one means four-on-three. So we had four where they had three because they had two where we had one.”

There was only one issue: Trey Kaufman-Renn, who was guarding Tugler, recovered slightly faster than Sampson hoped.

“This is a tribute to his basketball IQ,” Sampson said. “Had he not peeled back and taken Jo, Jo was getting ready to hammer that thing.”

But Tugler processed what was in front of him in a split-second, feeding the ball back to inbounder Milos Uzan for a wide open, last-second layup to give Houston the 62-60 win and a spot in Sunday’s Elite Eight against Tennessee.

“That pass that Tugler made? We don’t teach that,” Sampson said. “That’s instinctive.”

Not once in all the years Sampson had run 51 himself or seen it run by Skiles had the center made that pass back to the inbounder.

“I’m always looking around,” Tugler said after. “I know it’s 2.8 seconds on the clock, something’s got to happen fast.”

Great teams always seem to mirror their coach, and this was yet another example of how Sampson’s mind calms in hectic moments to find the simple solution.

Again and again throughout this postseason, he’s made the tweak that flips the game for his Cougars, whether it was ghosting ball screens against Arizona in the Big 12 tournament final, finding a way to get J’Wan Roberts to his left hand in a round of 32 showdown with Gonzaga or picking on Purdue’s drop coverage on Friday night, after the Boilermakers got the Coogs out of rhythm in the early going and took a 31-29 into halftime. For the No. 1 seed, it felt like a road environment — No. 4 seed Purdue had to travel only 66 miles from campus to Lucas Oil Stadium.

It was also not lost on the Sampson family that the Cougars’ regional assignment meant a return to the state of Indiana. Sampson was forced to resign as Indiana head coach in 2008 for impermissible phone calls to recruits and was given a five-year show-cause penalty by the NCAA, whose offices are just down the street from where Friday’s game was played.

That hiccup in his career is likely the thing keeping Sampson, who has won 796 games, nine regular-season conference titles, nine conference tournaments and two Final Fours, out of the Basketball Hall of Fame.

His son Kellen Sampson, an assistant and head-coach-in-waiting at Houston, replayed the final sequence in the coaches’ locker room late on Friday night and was asked if he wants to see his dad get to Springfield, Mass.

“I do,” he said. “One game.”

That would be the one on the final Monday of the season, a national championship providing the final line on the resume that would make his father a lock.

“We’ve been on the doorstep here the last five years,” Kellen said. “We’re here. Gotta cash one of them in. Just got to cash one of them in.”

It’s not going to be easy, with the other three No. 1 seeds all remaining in this top-heavy NCAA Tournament, along with three No. 2s and one No. 3.

But the 69-year-old might have a few more tricks up his sleeve than everyone else. Because he knows when to hold on to something for future use.

“Shoutout,” Sampson said before getting on the team bus, “to Scott Skiles.”

(Photo: Gregory Shamus / Getty Images)