Arsenal 2 

    * Watt 68,
    * Vela 76

West Brom 0 

Arsenal's latest crop of bright young things has another cup run to contemplate. A line-up crammed with teenage talent, with only a pair of wiser old heads at centre-half for company, eventually deflated the Championship's best, West Bromwich Albion, as they set about dazzling this competition yet again.

This was a sterner test than that posed by Sheffield United at the same stage last year but, aided by a misdemeanour from a former Arsenal youth team player, the hosts ultimately prevailed. There were flashes of impudent brilliance on show against impressive opponents left depleted by Jerome Thomas's dismissal for a first-half shove on Jack Wilshere, the hosts' neat and occasionally scintillating approach summed up by their decisive second goal.

Albion had been holding firm and even threatening an equaliser on the break when the home substitute Mark Randall, a player with experience on loan outside the top division, conjured a wonderful chip over Dean Kiely that cannoned down from the crossbar. A panicked Leon Barnett attempted to chest the rebound back to his goalkeeper only for Carlos Vela, another replacement, to nip in, poke the ball clear of Kiely's body and tap into the empty net. This may not have been as rousing as the 6-0 dismissal of United a year ago, but it was impressive nonetheless.

It was poignant that Arsenal had handed first-team debuts to Wojciech Szczesny, Gilles Sunu and Sanchez Watt, three of the eight teenagers in their starting line-up, on the day that their chief executive, Ivan Gazidis, had publicly flung his support behind Arsène Wenger's dual policies of youth development and restraint in the market. A quintet of other youngsters are currently on loan at other clubs. The cream of those who remain had their chance here.

"We believe transfer spending is the last resort," said Gazidis. "That's a sensible view to have. Re-signing existing players is a far more efficient system. What Arsène will not do is spend money on players that do not add something of real value. It's not easy for a club to walk this path when others have outside funding that we don't have. But it's a path we are committed to. Arsène thinks about the development of the team."

This competition has accelerated that evolution in recent seasons, inflicting regular dismissals upon Championship sides en route, though the education gleaned from ventures into the Carling Cup are clearly not always far-reaching. Albion, top of the second tier and resplendent while slaughtering Middlesbrough on Teesside at the weekend, had held firm when required and threatened reward aplenty at the other end until their own Arsenal youth team graduate rather undermined their challenge just before the break.

Thomas had won two FA Youth Cups with the north London club at the turn of the century and made a handful of senior appearances in this competition. Now considered a seasoned professional, he lost his composure too easily once Wilshere – claiming he had been elbowed – had abruptly rejected his hand after the pair had crumpled to the turf in a mess of arms and legs. The 26-year-old shoved the midfielder back to the ground and, while the Arsenal player's reaction may have been overly dramatic, clutching his forehead when contact appeared to be nearer his neck, the red card was inevitable.

The visitors will not have relished the contest at a numerical disadvantage. They had coaxed fine reaction saves from Szczesny, denying Simon Cox and Robert Koren, and seen Kerrea Gilbert scramble Cox's attempt from the goal-line when the Polish goalkeeper had been bypassed. Suppressing the home side's youthful exuberance with only 10 men suddenly appeared a daunting prospect.

The hosts had offered enough of a challenge when the visitors still boasted a full complement. Twice Philippe Senderos had flicked headers wide while Watt, a striker brimming with pace and raw ability, had dribbled Wilshere's pull-back onto a post as Dean Kiely retreated as if in slow motion to smother. There was busy invention from Aaron Ramsey and Sunu, and clever positioning and surety at the base of midfield from the composed Francis Coquelin, whose route to the first-team might be quickest among the new batch.

Yet Wenger's decision to introduce Vela as an older head reflected the reality that the Baggies, with Cox heading over then forcing Szczesny to save, remained potent opponents on the counter and Arsenal needed to chisel out reward before the contest drifted into extra-time. The Mexican's influence was virtually immediate. Latching on to Ramsey's lobbed pass, he cut inside Jonas Olsson and spat a shot that Kiely could only palm into the path of Watt. The 18-year-old, calm and assured, slid in his first senior goal with glee. Vela's own reward 14 minutes from time merely added gloss to the victory.

Sauce

Sir Alex Ferguson likes to boast that his Manchester United team score more late goals than any other side in the world. Others argue that they get a bit of extra help from referees. It has now emerged that the Premier League champions do, as suspected, benefit from an imbalance in the amount of stoppage time that is added to their matches.

After the controversy over Michael Owen's winning goal in Sunday's Manchester derby, the Guardian has looked at all of United's league matches at Old Trafford since the start of the 2006-07 season and discovered that, on average, there has been over a minute extra added by referees when United do not have the lead after 90 minutes, compared to when they are in front. In 48 games when United were ahead, the average amount of stoppage time was 191.35 seconds. In 12 matches when United were drawing or losing there was an average of 257.17sec.

The average stoppage time added at Old Trafford in the period in question is below that given at Anfield, the Emirates Stadium and Stamford Bridge. United's is 205 seconds, compared to Liverpool's 210sec, Arsenal's 224sec and Chelsea's 229sec. But there is also evidence to support the suspicions of many managers, players and supporters that United get preferential treatment at home. When Owen made it 4-3 on Sunday the game was five minutes and 26 seconds into stoppage time. In total, the referee, Martin Atkinson, allowed almost seven minutes, even though the fourth official had signalled a minimum of four. Mark Hughes, the City manager, spoke of feeling "robbed". His sense of grievance will not be helped if he analyses the last three seasons.

In 2006-07, for example, United were winning 15 times on entering stoppage time and referees added an average 194.53sec. In the four games when United were not winning there was an average of 217.25sec. The following year the disparity was greater, Opta's figures showing an average 178.29sec added when United were winning and 254.5sec when they were not. Last season it was 187.71sec compared to 258.6sec.

The pattern has continued in the first three games of the season. In the two games United have led they have played an average 304sec of injury time. On Sunday, Atkinson allowed the game to go on for 415sec.

Sauce