Marcus Rashford continued his rise to prominence by netting the only goal of the game in the 15th minute at Etihad Stadium as he coolly slotted home to put his side ahead.
And the Red Devils hung on to claim the victory and give their top-four hopes a significant boost.
Speaking on Sky Sports after the final whistle, Carragher said: “Louis van Gaal gets a lot of criticism for the job he’s done and the players who have come and gone.
“But he [Smalling] is one of the massive success stories of Van Gaal’s time at the club.
“He’s the leader at the back for Manchester United. Going into the summer, he is the standout England centre-back. He was outstanding today.”
The result was the perfect response from Louis van Gaal’s men, who headed into the game on the back of their Europa League exit at the hands of Liverpool on Thursday night.
The result leaves Manchester United in sixth place in the Premier League table and just one point behind City heading into the final eight games of the season.
United’s next game is a home clash against Everton at Old Trafford after the international break.
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