The Dutchman opened the scoring at Old Trafford six minutes before half-time and late goals from Zlatan Ibrahimovic and Henrikh Mkhitaryan helped clinch a 3-1 victory for Jose Mourinho's side.
After a shaky spell in September and October, United have hit their stride under Mourinho and are unbeaten in the Premier League for two months.
The manager was unhappy with their first-half display but Blind's goal settled the nerves and United missed several golden chances to extend their lead prior to Ibrahimovic's strike in the 82nd minute.
That was overshadowed six minutes later by substitute Mkhitaryan's spectacular flick, a goal almost matched in quality by Fabio Borini's volleyed consolation for Sunderland.
United remain 13 points behind leaders Chelsea and have four to make up on Arsenal in fourth but Blind has no doubt they are heading in the right direction.
He told MUTV: "In the second half we had difficulty getting the ball but after that second goal it became a lot easier for us. Sunderland didn't create many chances and we created good chances. So I think we did well.
"In the end it was a difficult game, we played very good and got the result. We didn't have a clean sheet but it's a good result and I feel confident to move forward like this.
"We have a lot of confidence now and we're in good shape. We need to work hard and keep that feeling up and win games. Of course we want to keep this run going and we'll work hard to do that."
Blind, brought into the side at the expense of Matteo Darmian, was an unlikely source for the opening goal but he timed his run into the area perfectly to meet Ibrahimovic's lay-off and find the far corner.
It was the full-back's first goal in 11 months and his first in the Premier League since September 2015.
Blind said: "There was so much space to run into and Zlatan gave me the ball, which was one touch and then a finish. It was a good feeling to score it and it was important to score before half-time."
The result meant Sunderland remain in the relegation zone, two points from safety, ahead of a crunch game against Burnley on Saturday.
The biggest disappointment for the Black Cats was that individual mistakes from Didier N'Dong and Jason Denayer led to United's second and third goals, killing the game when it had looked like Sunderland might find an equaliser.
Defender Billy Jones told safc.com: "Going in at half-time 1-0 down was disappointing. We talked about if we can keep it at that and stay in the game we've got a chance, and we also talked before the game about not giving Manchester United any easy goals.
"We feel like the second and third goals, that's what they were, with a couple of bad passes in the middle of the park to set them on their way.
"It's just disappointing that we've done well again against one of the big teams and haven't got anything to show for it. It makes the game against Burnley even more important now.
"We've got to show all the positives from this game and be more clinical when we have our chances, and obviously keep it tight at the back as well."
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