Wilkinson finished with 13 points, including a second-half try, but his late miss in windy conditions allowed Northampton to edge an entertaining game 25-23.
Fletcher, though, preferred to concentrate on Wilkinson's all-round performance and insisted Newcastle must not be just a one-man outfit.
"It is a team game," he said. "I thought he was very good. Unfortunately, he missed a couple of kicks but his work-rate is incredible and he is effective on the ball.
"If you actually analyse what he does in the game, if you look at the impact compared to any other player on the pitch - how far he runs, his tackles, his effectiveness - then you would be amazed.
"He has obviously been working hard during the time he has had out."
Northampton had stormed ahead on the back of dominant forwards performance in the first half that led to directly to a try for David Quinlan.
But Newcastle hit back from 13-3 down to take the lead with two magnificent tries.
Brent Wilson's break created an opening for Anthony Elliot to score and just four minutes later Wilkinson popped up to finish off a stunning break from Toby Flood.
After Northampton's forward laid the platform for replacement scrum-half Mark Robinson to draw the scores level, Newcastle led again with a try from flanker Ben Woods.
But they could not preserve their advantage and Northampton regained the edge when Bruce Reihana landed a touchline conversion following Ben Cohen's try in the corner.
It was enough for the win - but only after Wilkinson's uncharacteristic late miss - and Saints coach Paul Grayson was impressed.
"It was not how we wanted to get out of the blocks," he said. "We were comfortably in control without ever playing well. We contrived to almost give it away.
"You have to pick up your points where you can. No doubt there will be times this season where we play well and get beaten so I can't complain about the result.
"But I can complain about the performance. After half-time we put no shape on the game."