However, the Cats do not expect him to wear the green vest too often in the future.
Cats coach Chris Scott said the match committee thought making Johnson the substitute was "the best call for the day" and should not be seen as "a precursor to anything that we'll do in subsequent weeks".
He said the 31-year-old accepted the decision "like a good team man".
"It wasn't his preference but he came on and did a really good job for the team,” Scott said after Geelong succumbed to North by 16 points.
Whether the decision had an impact on the result is impossible to answer but Johnson performed well when he replaced key forward Josh Walker during the third quarter.
He grabbed nine disposals, recorded four inside 50s and kicked two last-quarter goals.
"I thought he was really valuable for us in a crucial stage of the game. [He] really gave us something but I wouldn't be planning on him playing that role too often," Scott said.
Although keeping the triple premiership player on the pine surprised even North Melbourne coach Brad Scott - who made some hasty planning to prepare for when Johnson did appear - the call is an insight into the Cats' determination to make decisions based on now rather than the past.
"You have to pick the team that you think is best served to win the game on any given day and we have been pretty clear - we're not prioritising the long-term future over winning every week but it is a consideration for us," Scott said.
In the first three weeks, the Cats' started first-year players Cory Gregson and Nakia Cockatoo as substitutes.
Meanwhile, Scott said inconsistency was the main concern for the Cats, after the loss to North Melbourne pushed his team to 16th on the ladder with just one win.
He said the team had performed reasonably well in parts but had been horrible at other times and bemoaned basic errors that led to opposition goals and halted the Cats' momentum.
A kick across goal from Mark Blicavs – a good performer overall - that gave North Melbourne its first goal was symptomatic of the costly errors that kept the Kangaroos in the game early.
However, Scott was still positive after the match.
"I'm not going to be drawn into any negativity after four rounds. We've played some pretty good teams. We play some pretty good teams in the next month or so as well … we just need to hang in there," Scott said.
"It's a fine line in modern footy and generally it's never as bad as you think it is if you just hang in and stay confident."
Scott said he had seen some good signs in some younger players and praised the performance of Jed Bews, who battled hard after receiving a corkie before half-time.
"I thought some of our young players showed some great signs,” he said.
“I’m not standing here saying we've got the best young players in the competition and we're flying [but] we've got some guys that are learning the way … there are some really good signs there and they play team footy.”