A Thomas Woodward brace wasn't enough to secure a point for Swansea City Under-18s as Colchester United claimed victory in their Professional Development League clash.
The hosts took an early sixth-minute lead through Jamie Arnold, before doubling their advantage just 10 minutes later through Ollie Godziemski.
Woodward scored either side of the break to bring the scoreline level, but the hosts netted late on through Makhaya James and James Sesere to seal the three points.
The Swans had seen goalkeeper Sam Seager return to the pitch for the first time in 16 months following a long-term injury.
Kai Rhodes had also been on course to make his first under-18s' start, but was replaced by Carter Heywood after suffering an injury in the warm up.
But it was the home side who made the better start and they got the opener following a scramble for the ball in the box, which ended with Arnold producing a composed finish.
Just 10 minutes later, a team move from the U's ended in a second goal. Caiden Lewis' long cross found James, whose delivery for Godziemski was met with an unstoppable finish.
Woodward halved the deficit just before the break. A switch of play from Jacob Cook into Cameron Llewellyn allowed the winger to beat his man one-on-one and cross for Woodward to convert.
The Swans also started brightly in the second period, and were rewarded with the equaliser approaching the hour mark.
It was Woodward, again, completing his brace to bring the visitors level after an error from Harrison Chamberlain in the Colchester goal.
But Colchester would regain the lead once more through James, who converted a cross from fellow goalscorer Godziemski at the far post.
And, deep into stoppage time, the hosts made sure of the three points as Sasere found the net with the last kick of the game.
The young Swans are in action on home turf for the final time this season in the south Wales Derby on Tuesday, May 7 (2pm) at Landore.
Colchester United Under-18s: Harrison Chamberlain, Bailey Berry, Makhaya James, Milton Oni (captain), Max Jolliffe, Caiden Lewis, Elkanah Akor, Kai Martin, Jamie Arnold, Burak Sabah, Oliver Godziemski.
Unused Substitutes: Jack Sexton, Alamin Kosoko, Alex Kokoshi.
Swansea City Under-18s: Sam Seager (Thomas Wright HT), Billy Clarke (Callum Deacon 58), Josh Pescatore, Jacob Cook, Iestyn Jones, Brogan Popham, Cameron Llewellyn (Milo Robinson 71), Harlan Perry (captain), Sammy Henia-Kamau, Thomas Woodward, Carter Heywood (Kaven Bloniarczyk 79)