Gareth Taylor’s young charges were dominant from start to finish in the showpiece final at the Riverside carving out a plethora of chances.
Ultimately though it was Nmecha’s superb 46th minute strike that proved the difference and ensured the silverware came to the CFA, the midfielder rifling home from the left flank after great work by Adrian Bernabe.
And the full-time whistle sparked scenes of celebration and joy amongst the players after a superb campaign that had begun back in September in the group stages.
On a cold but crisp evening on Teesside, the young Blues soon settled into their collective stride, dominating both territory and possession.
Despite enjoying home advantage, Boro mainly opted to field 10 men behind the ball and inviting City to probe for space and openings.
City then carved out our best chance of the opening half on 10 minutes. Nmecha delivered a fine left-wing cross after Adrian Bernabe’s shot had been blocked and found the unmarked Ben Knight eight yards out.
However, the winger’s header agonisingly went the wrong side of the left-hand post.
Young central defender Taylor Harwood-Bellis was an early source of much of City’s best work and from one of his trademark raking, long-range passes, Bernabe cut inside from the left wing but his pass to the waiting Nmecha was under-cooked.
It wasn’t all one-way traffic though and Boro served notice of their attacking armoury on 18 minutes when Stephen Wearne weaved his way past two City defenders before curling a right foot effort just wide.
Two minutes later Boro threatened again as Alberto Balde’s deft lob bamboozled the Blues defence to find Hayden Hackney clear in the box. Fortunately, though the linesman had flagged for offside.
But those proved the exceptions and on 22 minutes another raid by Taylor’s charges saw Bernabe feed Nabil Touaizi in the box. The Spaniard coolly brought the ball under control before swivelling and firing in a sweet half-volley which was gathered by Boro keeper Brynn.
The Blues came desperately close to forcing a breakthrough again on 39 minutes when Tommy Doyle was inches away from converting a superb 20-yard free-kick.
And City ended the first half as they had begun, knocking on the hosts door. From yet another left-wing forward foray, Nmecha fizzed in a teasing cross which evaded Touaizi and then frustratingly rebounded off the waiting Knight at the far post.
However, the Blues didn’t have to wait long after the restart before we made a deserved breakthrough.
It arrived on 46 minutes and Bernabe proved the architect, his weaving run opening up the Boro backline before he found Nmecha free on the left channel.
There was still to work to do but the youngster showed both skill and vision to drift inside two defenders before drilling a shot inside the right-hand corner for a wonderful strike.
The goal only added to the Blues’ confidence, but it also served to give hosts an added sense of urgency and there was a self-inflicted scare for City on the hour.
Goalkeeper Louie Moulden’s attempted clearance was intercepted by Hackney who drove forward before firing narrowly over.
Bernabe was a key figure in the second half and almost doubled our lead on 64 minutes after shimmying into space and powering in a shot which stung Brynn’s gloves.
Nmecha then nearly doubled his own tally after dipping his shoulders to open up the angle and unleashing a right foot stinger which Boro keeper Brynn could only parry.
Boro threatened again with 10 minutes left from a short free-kick with left back Jack Robinson’s strike forcing Moulden to gather at the second attempt.
City though should have put the game to bed on 83 minutes. Bernabe broke with a four on three advantage and Dele-Bashiru fed the waiting Henri Ogunby whose ball into the area found Knight.
His shot cannoned off the bar and there were appeals from City that the ball had crossed the line but referee Jonathan Urwin was unmoved and waved play on.
The Blues then opened up Boro once more with Ogunby’s shot forcing a smart save from Brynn.
In a pulsating finale Moulden then had to produce a fine punch clear from Robinson’s cross with Stephenson waiting to pounce and City’s hearts in their mouths.
Deep into stoppage time Doyle then drove forward before finding Knight who somehow fired over from close range.
But it mattered not as the whistle then sounded allowing the young Blues to celebrate a deserved trophy triumph.
And with a FA Youth Cup semi-final on the horizon there could be more success to come for Taylor's youngsters.
How we lined up
Louie Moulden was in goal shielded by a back four of skipper Rowan McDonald, Taylor Harwood-Bellis, Yeboah Amankwah and Alpha Diounkou. In midfield were Tommy Doyle, Felix Nmecha, Fisayo Dele-Bashiru and Adrian Bernabe. Upfront were Nabil Touaizi and Ben Knight.
Gareth Taylor’s side are next in action on March 30, ironically away once again at Middlesbrough, but this time for an Under-18 Premier League encounter.