Sir Alex Ferguson hailed his side's resolve and determination after ten-men United held on for a vital 1-0 victory over neighbours City.
Wayne Rooney's close range finish just before the break was the difference between the two sides, despite the Reds being a man down for the final 22 minutes following Cristiano Ronaldo's sending off.
The United boss was delighted with the victory which keeps the Reds within touching distance of Chelsea and Liverpool.
"We needed to win given our position behind the top two and it's a significant result for us," Sir Alex told MUTV.
"It was a fantastic performance particularly in the first half and with ten men the players showed their resolve and a great determination to see the game out.
"We defended well throughout and never really had any problems in that respect, but that was down to our good defensive play.
"Losing twice to them last season was something that's never happened during my 22 years here, and you don't forget these things. So we're pleased to get the result."
Sir Alex took time to pay tribute to United's match-winner after he notched his 100th career goal.
"Andy Cole was a tap-in specialist because he always anticipated situations and Wayne anticipated very well today," said the boss. "Scoring 100 goals is a terrific achievement, and his work-rate throughout was phenomenal."