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As a prospect at Lake Central, Gelen Robinson was timed at 4.79 seconds in the 40-yard dash, according to recruiting services.

The Purdue junior defensive end might not have been running with quite that speed on his 78-yard interception return for a touchdown Saturday against Eastern Kentucky. Or was he?

“That was 50 pounds ago,” Robinson joked after the Boilermakers opened their season with a 45-24 win at Ross-Ade Stadium. “Hopefully it was still around that time, if not faster.”

Either way, the 6-foot-1, 275-pounder — he was 250 even last season — had the wheels to take his first career interception the distance, with a bit of assistance.

Eastern Kentucky attempted a throwback to quarterback Bennie Coney. But with defensive tackle Jake Replogle applying pressure on James Smith, Robinson stayed home on the back side, as taught by defensive line coach Randy Melvin.

Robinson snagged the floating pass and motored down the right sideline, with cornerback Myles Norwood blocking a pursuing Coney. Robinson pulled away the last 30 yards as Coney stumbled to the ground thanks to Norwood.

Robinson’s highlight-reel play gave the Boilermakers a 21-0 lead with 3:31 left in the first quarter.

“As soon as I saw the quarterback flare out the opposite way, it’s pretty much my job that coach Melvin coached me to do,” he said. “I thought I was running fast, but I had a little help from Myles blocking the quarterback, and that was a huge part of scoring. All I could really think about was getting to the end zone and keeping my head down and my feet moving.”

Coach Darrell Hazell enjoyed Purdue’s first pick-six by a defensive lineman since Cliff Avril’s 43-yarder at Minnesota in 2007.

“It was an awareness play,” he said. “He just felt it. Some football instincts kicked in. You always worry about those big guys being able to catch. But he made the catch and did a good job finishing.”

Robinson did well starting against Eastern Kentucky, having been listed as a backup. But Austin Larkin was sidelined after injuring his left ankle Thursday, and he was wearing a boot Saturday.

Robinson opened training camp at No. 3 on Purdue’s depth chart after starting seven games last season. The situation wasn’t easy.

“It was a little challenging,” he said. “But I know it’s all about competition. It’s not personal. Austin’s great. He’s one of the best athletes I’ve seen. We have some great D-linemen and D-ends.

“The coaches are going to do anything to help the team win. If that means putting someone in front of me, that’s what it takes. It was a humbling experience, and I’m just ready to keep moving this season.”

So are the Boilermakers after playing their final game against a Football Championship Subdivision opponent. They posted nice numbers against Eastern Kentucky but also understood the context.

Markell Jones ran for 145 yards and a TD on 24 carries and had four catches for 24 yards. David Blough completed 25 of 43 passes for 245 yards with one TD and one interception, and he ran for two 1-yard scores.

Robinson’s interception was Purdue’s third takeaway in the first quarter alone, and the Boilermakers added a fourth in the fourth quarter.

Four of Purdue’s seven wins under Hazell have come against FCS teams. With the Boilermakers playing Cincinnati next week, he expects success against Football Bowl Subdivision teams.

“We’re a different football team,” Hazell said. “We’re a different mindset, our makeup’s different, we have better players. It’s been three years to get to this point.

“There were times in similar games where we tightened up, and we were in a dogfight those last three or four minutes. It was good to see us respond the way we did.”

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Twitter @MichaelOsipoff