The Canaries created a number of good opportunities during a frustrating afternoon at Carrow Road, but were punished for their profligacy when Wayne Rooney capitalised on Sebastien Bassong's error to tee up Juan Mata, who slotted home 18 minutes from time.
And having seen the likes of Cameron Jerome miss some good opportunities either side of half-time, Norwich were once again left to rue their shortcomings in front of goal, with Pinto admitting it was the key difference between the two sides.
Speaking to Norwich City TV after the game, Pinto said: "It’s disappointing because we did a lot to win the game.
"Our supporters were very good and made it an unbelievable atmosphere. We started the game very well to create chances, and in the end probably didn’t deserve the result we got.
"That’s the big difference between us and other teams. We had the chances but we weren’t able to score, then Manchester United had one great chance which they scored from.
"It was that which was the difference in the game."
The Canaries host Watford at Carrow Road on Wednesday evening, although Sunderland's surprise 3-2 win over Chelsea means their fate is now out of their hands.
Their relegation will be confirmed if Sam Allardyce's men can get a result at home to an out-of-form Everton, with the Wearsiders needing just one more win from their two remaining games to preserve their top-flight status for another season.