CARNOUSTIE, Scotland — Keir McNicoll, a 34-year-old assistant pro at Carnoustie, had the day of his life Saturday.

He played in a British Open on his home course.

There will be no official record of the 18 holes McNicoll played in Saturday’s third round, because he played as a marker — not as a competitor — to even out the remaining field after Friday’s cut,

No matter, though: This was a day of a lifetime for McNicoll as he played alongside Gavin Green in the first tee time of the day since there was an odd number of players who made the cut.

“I dreamed about playing in The Open as a kid, so I was properly emotional on the first tee,’’ said McNicoll, who said he’s tried to qualify for Opens about six times with no luck. “If I had qualified here, I don’t know what I would’ve done. I’ve caddied before, back in 2005 at St. Andrews for Eric Ramsay, which was amazing in itself as it was Jack Nicklaus’ last Open. It was brilliant caddying for one of my best friends in Eric, but this kind of trumps it.”

McNicoll, who was born in Carnoustie, had his sister, Katy, caddying for him. She’s an assistant pro at Gullane, where the Scottish Open was played last week, and she caddies on the Ladies European Tour.

He called his moment on the first tee “scary,’’ adding, “I was a bit emotional. “But to walk out with those hundreds of people watching and cheering was so cool. It’s the hardest round I’ve ever played out here. I’m not playing that well, so just to get it airborne off the first was great.’’

McNicoll said he shot about 80, with a birdie on No. 3 and a quadruple bogey on No. 8.

As long as no player withdraws before Sunday’s final round, McNicoll will get another chance as the marker. He’s scheduled to play with Beau Hossler in the morning.

“Unless someone throws me out, I’ll get another crack at it,’’ he said.

Green was glad to have McNicoll.

“It’s better to play with somebody than not to play with anybody,’’ he said. “You play alone and you just feel so lonely. It’s like your dead out there.’’