Graham Dorrans and Brian Gilmour scored for the Scots

Midfielder Jamie Adams gave the home side a first-half lead when he headed in from a Ryan Conroy corner.

Rory McAllister fired home from close range after a cross from fellow substitute Brian Gilmour at Firhill.

Substitute Graham Dorrans curled in the third after 75 minutes and Gilmour drove in the fourth.

Interview: Scotland U-20 manager Archie Gemmill

Interview: Scotland U-20 players Scott Cuthbert and Mark Reynolds

The young Scots had six regulars missing from their squad but still proved too strong for their older opponents.

Archie Gemmill's side had the best of a sedate first half against their spirited but limited visitors.

Ross Campbell had already screwed a shot wide by the time Adams rose highest in the six-yard box to glance a header past the helpless Jonathan Tuffey after 11 minutes.

Partick Thistle goalkeeper Tuffey pulled off saves on his home ground from a Conroy volley and Campbell when the striker was through on goal.

Both sides reshuffled at the break and it was the Irish who initially adapted better, Kyle McVey going close with a header and Rory McArdle firing just wide with a spectacular overhead kick.

But Gilmour, who had replaced Conroy, fired in a cross and McAllister scooped the ball in to the net from close range.

Dorrans, who had come on for Andrew Considine at the interval, curled in number three from the edge of the box.

And Gilmour drove home the fourth from 20 yards out seven minutes later.

Scotland U-20 coach Tommy Wilson: "It was beyond what we could have hoped for given the week we've had with call-offs and injuries.

"I thought the result reflected the performance.

"We need to name a squad of 30 and no-one has ruled themselves out after this performance. In fact, some have made it blooming hard for us.

"It's a nice place to be. I just hope the players will come back fresh after a four or five week break."

Northern Ireland Under-21 boss Roy Millar: "It was an interesting game.

"For an hour, it was very competitive and could have gone either way.

"Unfortunately, we stopped playing and stopped defending.

"For the last half hour, Scotland's passing and movement was very good.

"They are a good side and showed why they are going to Canada."