The Red Devils thrashed the Magpies 4-1 at Old Trafford this weekend, with the likes of Zlatan Ibrahimovic and Pogba returning to action after long-term injuries.
Pogba missed 12 games with a hamstring injury, a spell during which United have slipped eight points behind leaders Manchester City.
"He affects our football", Mourinho said of Pogba.
"We lost a bit of that because, while other players are good players, they have different qualities".
"We knew that was a massive difference between both teams".
Before that they face a trip to Basel in the Champions League on Wednesday.
"If I don't believe that [United could win the league], I'd stop playing".
Arsenal aim to end six-game winless Premier League run vs
Alexandre Lacazette was heralded as the saviour of Arsenal when he was brought into the club from Lyon during the summer. They enter Saturday in danger of doing that for the first time this year, having also lost at Old Trafford on October 28.
"And at the end, we see the result".
Nevin told Newstalk: "The physical prowess they've got to come back in [Pogba and Ibrahimovic], they'll be fine at home, they'll get top four". This was not a one-man work, it was everyone's and thanks to them that I am back on field and can play because if people knew the real injury they would be in shock that I was even playing.
Chris Smalling headed in another fine Ashley Young cross to make it 2-1 just before half time, before Pogba got one for himself as the home team dominated in the second half, knocking in the ball after Rashford cleverly headed a Romelu Lukaku cross into his path. I think there is a possibility for winning everything. "We had control, we had goals and attractive actions".
Rafa Benitez was forced to watch as Pogba left Isaac Hayden for dead to stand a cross up for Anthony Martial's goal and he also left the former Arsenal man lagging behind as he strolled onto Marcus Rashford's knock-down to score.
The Red Devils made a brilliant start to the 2017-18 season following six victories and one stalemate in their opening seven games.
Newcastle striker Dwight Gayle showed why he should be in the starting 11 with his team's only goal this evening.