Ashley Young opened the scoring for the Premier League champions early in the second half, before Javier Hernandez sealed victory five minutes from time to give Ajax a mountain to climb at Old Trafford next week.
Despite the win, Ferguson was less than pleased with his side’s first-half performance at the Amsterdam Arena.
The United boss said: “I’m delighted with the score line, but I think it was a very ordinary performance by us. We didn’t reach any great heights in the game, but we did improve in the second half and we probably deserved to win it.
“In the first half we didn’t play well at all, there was no rhythm to our game. I know Ajax can make it very difficult with the system they play because they close the midfield out very well and the press the ball really well.
“There was no tempo to our play in the first half. In the second half we improved a lot, made some good chances but it wasn’t a good performance from us.”
Half an hour into the lacklustre first half, David De Gea kept out a superb strike from Siem de Jong.
Ajax had a strong penalty claim on the stroke of half-time after Rio Ferdinand appeared to have brought down Miralem Sulejmani inside the area, but Italian referee Gianluca Rocchi dismissed the Dutch side’s appeals.
United began the second half the brighter, with Wayne Rooney and Hernandez causing problems for the Dutch outfit’s defence.
Just before the hour mark, United’s pressure was rewarded as Young fired in the opening goal.
A low cross from Nani fell to the former Aston Villa winger, who skipped inside past Vurnon Anita and drilled the ball through the legs of Kenneth Vermeer.
With less than 10 minutes to go, Rooney and Hernandez combined to allow the Mexican international to kill off the match.
Ferguson highlighted how important the second goal was away from home, but stressed the Dutch side will still be a threat.
He said: “The second goal we scored gives us a good opportunity because, not taking anything for granted, we’re at home at Old Trafford and this gives us a great chance to progress to the next round.”
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