Sir Alex Ferguson felt the understanding of Rio Ferdinand and Nemanja Vidic was the key to his side's 1-0 win at Porto on Wednesday night that secured their place in the Champions League semi-finals.
Cristiano Ronaldo scored the only goal of the game in the sixth minute and United had to withstand a lot of pressure after going into the match on the back of a 2-2 draw at Old Trafford last week.
Ferdinand had been a doubt for the game with a back injury but he teamed up with Vidic to again form a formidable partnership.
Ferguson told Sky Sports: "They did well. We showed good concentration at the back and defended very well.
"If we get back to that foundation of not conceding goals, we can do well. We had stability at the back with the recognition of Ferdinand and Vidic and that was a great start.
"I couldn't see the dangers. I thought we controlled that part very well. Nothing really bothered us."
Ronaldo's goal was a phenomenal strike from fully 40 yards.
"It was a magnificent goal, a fantastic hit," continued Ferguson. "It took them by surprise, the keeper had no chance."
United will now face Arsenal in the last four, and Ferguson added: "It's going to be a great semi, there'll be some good football in that one."
Meanwhile, Ronaldo is hopeful the battling victory will help United emerge from the sticky patch of form they have been in since losing 4-1 to arch-rivals Liverpool in the Premier League
"This will give us confidence," he told Sky Sports. "The last five games we didn't play great and I hope this will change that."
Describing his goal, the Portuguese forward said: "When Anderson gave me the ball I think straight away to turn and shoot in the goal and I score a fantastic goal."
"It is the best I have scored," he said.
"It was a fantastic strike and I can't wait to see it again on DVD. I am very happy with it."
Ronaldo, who joined United from Porto's rivals Sporting Lisbon, is expecting an exciting semi-final.
"It's a fantastic thing," he said of the tie. "Arsenal play fantastic football. It'll be a tight game. We know each other and I hope to win the tie and go to the final."
Porto assistant coach Jose Gomes, standing in for Jesualdo Ferreira who watched the game in a secret location after being banned by UEFA yesterday, felt the hosts had been unlucky.
"It was not a fair result," he said. "We did really well at Old Trafford but the ball just would not go in for us this evening."