After a goalless first half at Old Trafford, the 18-year-old’s cross led to Antonio Valencia’s opener in the 47th minute.
On a personal level I’ve worked hard to get back. Hopefully there is more to come for me
And the midfielder was again involved in the build-up as Danny Welbeck fired Patrice Evra’s cross home in the 59th minute to hand United’ their fifth win in six league games.
And Fletcher was full of praise for the highly-rated Januzaj after the final whistle.
“He made the difference,” Fletcher told Sky Sports.
“He’s a young lad but he’s come into the team and has been a revelation this season. We know how good he is at dribbling and making things happen.
“We wanted to get the ball to him as much as we could. We did that, and he didn’t disappoint.”
United stay in seventh place in the Premier League table, nine points behind leaders Chelsea.
And Fletcher continued: “I think that we raised the tempo second half and that was the difference.
“We know teams like Swansea like to keep the ball.
“We have a lot of players in midfield. You want to press but you can’t sometimes. Ultimately if you want to win the game you have to get up for the ball and that’s what we did. We have to back it up but you need to win every game at Manchester United.
“On a personal level I’ve worked hard to get back. Hopefully there is more to come for me. I’m happy where I am right now.”
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