The relief on Carlos Tévez’s face said it all, a first goal for almost two months lifting a weight off his shoulders and securing Manchester United a place in the Carling Cup quarter-finals last night, but that elation may quickly have given way to a familiar sinking feeling.

This might have represented a return to form of sorts for Tévez, but the Argentina striker’s reward for eventually seeing off an obdurate Queens Park Rangers team is likely to be a place back on the substitutes’ bench at home to Stoke City in the Barclays Premier League on Saturday.

It must be a dispiriting thought, but Tévez will at least take some comfort from only his second goal of the season, even if it was in keeping with the Argentinian’s troubles that it took another striker to turn this tie in United’s favour.

QPR were hanging on for dear life by the time Danny Welbeck was brought on in the 72nd minute, but having withstood a siege, thanks mainly to Radek Cerny, their goalkeeper, the Coca-Cola Championship team looked as though they were going to take a one-sided contest into extra time.

Welbeck, though, had other ideas. The 17-year-old forward, making his second competitive appearance for United, had been on the pitch only four minutes when he won the penalty, after being tripped by Peter Ramage, from which Tévez calmly claimed the decisive goal.

“Danny is an exceptionally talented lad and he came on and made a difference,” Sir Alex Ferguson, the United manager, said.

How QPR had survived that long is anyone’s guess, even if Cerny looked far better than he ever did for Tottenham Hotspur. It was only when a goal down that the visiting team found the confidence to venture out of their own half and start asking United a few questions, so much so that Ferguson had to throw on Nemanja Vidic to shore things up.

Emmanuel Jorge Ledesma squandered a great chance to take the game into extra time when he snatched at a shot from ten yards and QPR also had a goal disallowed for offside, but otherwise they were non-existent as an attacking force.

United missed a hatful of chances, Tévez forcing a fine reflex save from Cerny and Park Ji Sung crashing a blistering 20-yard drive against the inside of a post in the second half, with Ferguson again left to bemoan a wastefulness that is fast becoming a fixture of their campaign. “We had a lot of chances in the game but at this moment they are not going in for us, but they will come all right,” he said.

Ferguson made eight changes to the team that lost 2-1 to Arsenal at the Emirates Stadium three days earlier, once again electing to give youth its chance in the competition, but it says everything about the gulf between the Premier League and the Championship that a team placed seventh in the second tier should be run ragged by a bunch of kids, albeit very talented ones.

It is to be expected that teams approach matches against United at Old Trafford with a degree of caution, but QPR sat back so deep that by midway through the second half they were inviting wave after wave of attacks.

United’s best chance came just before the hour. Rafael Da Silva appeared to be going nowhere when he was sandwiched on the touchline by two QPR defenders, only for the Brazilian to dart between his markers and slip the ball to Park, whose shot cannoned off the far post.

Cerny then reacted superbly to tip over a venomous close-range effort from Tévez, who, for all his running, lacked the cunning that he needs to rediscover if he is to usurp Dimitar Berbatov or Wayne Rooney from the first team.

Tévez did exchange a lovely one-two with Anderson in the first half that almost brought a goal for the Brazilian, excelling in an advanced midfield position, but Tévez’s evening was characterised more by endeavour than anything else. Chances were plentiful; Anderson, who, for all his talent, has now gone 51 matches without a goal for United, twice testing Cerny.

Never mind who wears the United shirt at the moment, goals are proving more difficult to come by than Ferguson would like. Just ask Tévez.

Manchester United (4-2-3-1): T Kuszczak — Rafael da Silva, G Neville (sub: N Vidic, 89min), J Evans, J O’Shea — D Gibson, R Possebon (sub: D Welbeck, 72) — Park Ji Sung, Anderson, Nani — C Tévez. Substitutes not used: B Foster, M Carrick, Manucho, T Cleverley, D Gray.

Queens Park Rangers (4-1-4-1): R Cerny — P Ramage, F Hall, D Stewart, M Connolly — G Mahon — M Rowlands, A Buzsaky (sub: P Agyemang, 33), D Parejo (sub: E J Ledesma, 46), L Cook (sub: S Di Camine, 78) — D Blackstock. Substitutes not used: J Cole, D Delaney, K Gorkss, H Ephraim.

Referee: P Dowd.

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