George Watson's College, the defending champions, claimed a third successive Brewin Dolphin Under-18 Schools Cup last night after defeating Merchiston Castle School 23-17 on the international pitch at BT Murrayfield.

Merchiston had earlier picked up the under-16 cup with a last-gasp 25-24 victory over Dollar Academy.

Watson's lost their towering lock Rory Evans to injury in the warm-up but despite being further handicapped when prop Calum Eastwood succumbed to a head injury early in the first half, they outplayed Merchiston with clever handling complemented by ferocious defence.

"The character this team showed was unbelievable," said Ally Donaldson, Watson's coach. "We lost a second-row in the warm-up and then a prop early in the first half but the boys were not fazed and we managed to fix the set-piece at half-time. I'm not sure if I've ever seen a more gutsy performance" .

Watson's trailed 5-3 at the interval, stand-off Kerr Stoddart having supplied the game's opening points with a penalty goal and centre Stafford McDowall having run in a try for Merchiston.

Then, in the second half, Watson's effectively won the game with three tries, the first from winger Calum Fox and then two from their Scotland Under-18 cap Robbie Nairn. Stoddart converted Nairn's second try and then added a penalty for what seemed an unassailable 23-5 lead. But in a show of defiance, Merchiston hit back with late tries by winger Louie Tang and replacement Tom Bisset, the latter converted by scrum-half Dan Nutton. However, it was too late to stop Watson's from taking the honours.

Scorers George Watson's College Tries: Nairn (2), Fox. Cons: Stoddart. Pens: Stoddart (2) Merchiston Castle School Tries McDowall, Tang Cons Nutton

In the under-16 final, Dollar Academy appeared to heading for victory when they led 24-20 with two tries apiece from stand-off Grant Hughes and wing Rory Cooke and two conversions from Hughes.

But with full-time showing on the clock, Merchiston winger Mackenzie Cox touched down to give his side a dramatic 25-24 win. The other Merchiston tries came from centre Hamish Scanlon and No.8 Tyler Thomas with stand-off Ronan Dowds converting two of his side's tries in addition to kicking two penalty goals.