Murty's Rangers reserve side beat the Hoops 2-0 at Firhill today to move within two wins of a league title.
Glenn Middleton scored twice and Celtic's youngsters had no response, despite having a number of players with first-team experience.
Johnston has netted three Premiership goals in five senior outings for Celtic this season, and Murty has revealed after the game that his players acknowledged the 19-year-old's threat during half time following a goalless first half, when Murty asked his troops what they thought was going wrong.
He told Rangers' YouTube channel: "When they came back with 'we have to be tighter, we have to be a bit more composed in final execution of the pass' and they were right. We needed to lock down there left side, because Mikey Johnston is a good player.
"We needed to be better and be a little more brave. They came up with that. The players had the answers."
Johnston is of course a big talent at Lennoxtown, and former manager Brendan Rodgers, who quit the Bhoys in February, said in January that he was an 'electrifying' player [The Record].
The arrivals of loanees Oliver Burke and Timothy Weah killed Johnston's chances of having a prolific second half to the season with the Bhoys, but both are likely to be gone by next season and it'll be interesting to see if he can kick on then.