Herrera has found himself down the pecking order at United since the summer arrival of Nemanja Matic, making just one Premier League start for the club so far this season.
The Spaniard was once again overlooked for today's game against the Toffees as Marouane Fellaini was chosen to replace the injured Paul Pogba, but he did make an appearance off the bench and Mourinho talked up the midfielder's importance to his side's performance.
"I think if the result was two or 3-0 after 30 minutes I would say a clear reflection of fantastic football we played in the first 30 or 35 minutes," he told reporters.
"Ultra dominant against a team that played with five, with four, and was difficult to play against, I think we played phenomenal in the first half-an-hour. Then they improved, they had a little bit more initiative, they bring a few more bodies into attacking areas, and they create us a couple of problems.
"But then I think Ander was important, he gave us the stability that we were losing a little bit and then was only possible, in my view, 1-0 or 2-0, I never thought in the last 15 or 20 minutes it could be 1-1. The 2-0 come and after that the third and fourth goals are just a consequence of a team that was sad and another team that was happy, for me the third and fourth goal were a little bit out of context in the game."
United have now won all four of their home matches this season without conceding a goal.