Two goals from striker Ewan Henderson helped Celtic come back from a goal down to beat Manchester United 3-1 in the Super Cup NI curtain raiser.
Ethan Laird opened the scoring for United after 52 minutes before the Scots hit two goals in three minutes.
Irish substitute Thomas Caffrey equalised in the 75th minute before Henderson capitalised on a goalkeeping error to put Celtic ahead.
He then finished off a late breakaway to seal the challenge match win.
The Under-19 match at the Coleraine Showgrounds opened the 2018 Super Cup NI, which starts on Monday.
Henderson the hero as Celtic persistence pays off
After a scoreless first half, it was United who struck first through attacking full-back Laird.
Celtic failed to clear after goalkeeper Ryan Mullan had saved superbly from United winger Largie Ramazani, and the ball made its way to right-back Laird, who had popped up on the left wing.
He showed the skills and footwork of a winger to cut inside a defender and drill a well-placed shot in at the near post.
The Glasgow giants had been well in the game until then and their persistence paid off when Caffrey curled a beautiful left-foot shot past substitute goalkeeper Jacob Carney to equalise.
They were ahead two minutes later when a poor goal-kick by Carney was closed down in midfield and the lively Henderson, who made his senior debut in May, scored with a shot that deflected off Di'shon Bernard.
As United pressed for an equaliser, the Scots mounted a breakaway attack in the 87th minute and man-of-the-match Henderson slotted home under Carney.
United's long history with the competition
After a two-year absence, United made a successful return to the Super Cup NI in last year's challenge match when they defeated a Northern Ireland select side 1-0.
The club has a long history with the competition, formerly called the Milk Cup, reaching 13 finals and winning six titles in its 35-year history.
Former United full-back and current England women's manager Phil Neville was in the crowd for the match.
He had hoped to watch his son Harvey, who is a member of the Manchester United squad, but he failed to get international clearance to play in the game.
Celtic's only previous appearance in the Super Cup NI came in 2016 when they took part in a four-team Under-21 tournament, beating Real Sociedad but losing to Everton in the final.
The competitive action in the Super Cup NI minor, junior and premier sections gets under way on Monday.
The teams will take part in an opening parade through Coleraine town centre on Sunday at 19:00 BST, with a welcome ceremony at the Showgrounds where former Northern Ireland international Gerry Armstrong will open the event.
The BBC Sport NI website will have live coverage of 13 games during the major youth tournament.