"We set up really well and we matched up really well against them", Lascelles added.
The victory pushes Newcastle up to 13-place in the Premier League but Benitez's side are still in the thick of it as they sit just two points away from the last relegation place which is occupied by Southampton.
"It was a huge win, but it wasn't a shock for us" said the 24-year-old to the Northern Echo, "Most games we have played this season, we have been really good". We will have some limitations and some problems, but you could still see this was another game when they were giving everything, and that is the positive thing. In the last few minutes, we were trying to defend and play on the counter-attack, and we did that, more or less, well.
"Hopefully it will not be my biggest win with Newcastle, hopefully we will have bigger wins than this one", said Benitez.More news: What direct rule in Northern Ireland means for the UK
And yet, somehow, they have remained second throughout most of the campaign - a sign of the natural talent and winning nous in the side as well as the fallibility of teams like Chelsea, Tottenham Hotspur, Arsenal and Liverpool.
"The way we were playing, with everybody giving everything, was absolutely fantastic".
Rafa Benitez's side claimed their first home Premier League win in nearly four months on Sunday.
Newcastle took the lead at Old Trafford in the reverse fixture before a rampant United side responded with four goals to claim all three points.More news: President Trump signs proclamation honoring victims of deadly Florida school shooting
"We did well, although still we were a little bit lucky at the end". "That is it. We were very close in a lot of games, but we were unlucky".
With 11 games to play, Newcastle are 12 points from the traditional 40-point safety mark.
But the cold reality is that United, with 27 games of the season gone, still don't have a known best starting XI, or even a formation that Mourinho and his staff have agreed upon.
"We've had good moments, bad moments, like every team".More news: Alzheimer's disease reversed in mouse model
"We did it most of the time, and at the end we got that goal and we defended as a team".