The Baggies boss read the riot act to his players in the dressing room after catching one of them on the phone checking out scores from the earlier games.
It's a result which leaves Albion on 40 points.
"I actually went mad before the game because one of the lads had his phone on looking at results. It's a difficult time to play. The lads were getting distracted and I went berserk.
"Irrespective of the other results it was always about what we do.
"Beating any of the top four or five teams is brilliant and something the players will take on board. But it's not the first time we've beaten United, many of the lads were part of the side that did it last year."
Speaking about the referee's decision to award a second-half penalty, after Saido Berahino was deemed to have handled the ball, Pulis added:
"It wasn't a penalty. That was disappointing. It looked outside the box to me.
"The linesman is five yards away and gives a corner, the ref is 25 yards away and gives a penalty.
"But credit to Boaz for the save."
Pulis felt his side deserved the victory:
"To come here you have to be resilient. We worked very hard to make sure people were in the right slots, make sure we were in good positions, good areas. But we also needed a bit of luck. And we had that.
"It's now 10 clean sheets since I arrived. But the key to staying up is to get points.
"This is a massive, massive result for us."