Mourinho's Manchester United side stunned the league leaders with a 2-0 victory at the weekend, which helped the Red Devils exact revenge for the two previous wins Chelsea managed to secure over the club this season.
The first of those was a comfortable 4-0 league win for Chelsea at Stamford Bridge in October before the Blues narrowly secured a 1-0 victory in the FA Cup in March thanks to N'Golo Kante's goal.
Mourinho, however, reacted to those two results by sending his side out to contain Eden Hazard while urging his forwards to finish off their chances - which they did when Marcus Rashford scored in the seventh minute before Ander Herrera ensured the three points with his goal four minutes after the break.
Nevin wasn't surprised to see a reaction from United at Old Trafford, and believes Mourinho used his inside knowledge of the players' strengths and weaknesses to trump his former club.
Writing in his column on Chelsea's website, Nevin said: "I have to say I was surprised by how shocked people seemed to be by the result on Sunday at Old Trafford.
"It is worth getting it straight, Man United are on a monumentally good run without defeat. For all that they draw too many games, they have the biggest squad in terms of quality in the league and they were playing at home.
"They had everything to play for in that they are striving for that Champions League place, which I have always felt they will get, and have a manager who is quite good technically and tactically!
"Actually he is better than quite good at the tactical side as we know more than anyone, but his inside knowledge of the Chelsea team was the killer on the day.
"He knew where to strangle our creativity and he managed to fire up his own players. On top of that they got lucky with both goals for different reasons (if the referee has missed Herrera’s hand ball in the build-up to the opening goal, the officials helping him surely must have seen it) and our lads had something of an off day as a group, not helped by Thibaut Courtois and Marcos Alonso being unavailable.
"In short, it was a perfect storm with so much to contend with and who said it was going to be easy anyway?"