It has contributed to a positive start to this year's RaboDirect PRO12 campaign, with Glasgow picking up six wins already to head into the international break in second place.
And the trio is in stiff competition for the Scotland shirt, along with Edinburgh youngster Grant Gilchrist, Montpellier's Jim Hamilton and British & Irish Lion - and Jonny's brother - Richie Gray.
Kellock, the most experienced of the group with 55 caps to his name, is aware that one indifferent performance could be enough to see a starting berth snatched from him.
"We're now looking back and seeing these young lads coming up, and they are doing very well, but I use that to push me forward," he told The Scotsman.
"They are here on merit. Jonny Gray, for example, has been exceptionally good for Glasgow and I'm sure he will get an opportunity over the next couple of weeks to show what he can do, so the guys playing against Japan have to perform.
"The simple fact is that with that level of competition, if you don't perform well in this game it may be your last.
"The competition has always been reasonably healthy. When I first came through we had Scott Murray, Stuart Grimes, Nathan Hines and Jason White, and myself and Jim have had a fairly good rivalry in recent years, on and off the park."