In the third period of the Caps' tilt with the Oilers in Edmonton, Corey Perry snuck one by Thompson's right shoulder to make the game 3-2 ... but immediately after the score, the goalie argued it shouldn't count.

Thompson pointed at a plate of nachos that had been chucked onto the ice just seconds before Perry unloaded a slap shot -- making it clear the queso bites distracted him.

The refs, though, saw things differently ... and allowed the goal -- much to Thompson's dismay.

Somehow, Thompson and the Capitals kept their cool and held on to win ... but afterward, the 27-year-old was pretty miffed over the situation.

"I've never seen that before," he said ... before adding, "Obviously, I've got to play to the whistle. That one's on me."

Thompson's coach, Spencer Carbery, had some similar feelings on the matter ... though he was at least able to laugh off the incident.

"I don't think I've ever seen a nachos-on-the-ice National Hockey League game," he said. "Did they save them? Maybe we can bring them into the locker room."

FYI, NHL rules state play should be stopped if objects are thrown onto the ice during play ... but only if they affect "progress of the game." Perry said after he "didn't even see" the fan's dinner before he shot the puck ... so the action carried on.