The young Argentine has caught the eye since replacing Logan Sargeant at Williams, with Red Bull reportedly interested.
However, in Lusail, he caught their Mexican star Perez sleeping.
Colapinto was starting dead last and in the pitlane with Perez as both teams altered their cars in parc ferme.
However, when it came to lights out on Saturday afternoon, the Red Bull star appeared to forget he was racing at all.
With the lights turned green, he sat still allowing rookie Colapinto to complete a swift overtake on his experienced foe.
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He held the position too, finishing 18th, while Perez finished last.
And the incident didn't go down well with Red Bull team boss Horner.
"I need to have a chat with him about it because it just looked like he was caught napping a little bit and obviously Colapinto got the jump on him," he told the official F1 channel.
Meanwhile speaking to Sky F1 he added: "I don't know, to be honest.
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"I need to have a chat with him about it. It looked like he just misjudged it.
"But when the light goes out, you're supposed to go."
"We managed to get some useful data from Checo in that race," Horner added.
"We managed to change the nose as well so we got some good feedback that hopefully we can use for [qualifying]."
"Basically, on a day that we weren't going to score points with him, it was better to get as much knowledge as we could," he explained.
"So that's what we've done, we've got some data now to look at between now and the next session, so hopefully we can make good use of it."
Perez himself, who finds his position at Red Bull under serious threat due to underperformance, insisted he had wanted clear-air ahead of him as he sought data to help the team.
"The main objective of today was to be as further back as possible, to have as much clean air as possible," he said after the sprint. "That was the objective.
"I think we managed to understand the car with the changes we've done. I think there is some room to improve what we have to do going forwards.
"We we have to try and bring a little bit more balance to the car."
But Colapinto himself was happy to catch Perez sleeping.
He joked: "Checo was... I don't know, he was looking at the traffic light or something. He was trying to get in first, sometimes he's a little late in the first one, you know?"