The former striker, who notoriously played for both Glasgow clubs, was hugely impressed with the Gers in the Hampden Park clash.
Former Celtic and Rangers striker Mo Johnston has told the Scottish Sun that Rangers will only keep moving forwards under Mark Warburton as long as they strengthen in the summer, but believes the Scottish Cup semi-final defeat shows that Ronny Deila has to go as Celtic manager.
Despite the division's difference between the two clubs, it was the Gers who emerged victorious from the hugely anticipated Old Firm clash at Hampden Park on Sunday, winning on penalties after a thrilling 2-2 draw over 120 minutes.
Though not likely to be a completely accurate indicator of what can be expected when the clubs renew their rivalry on a permanent basis next season, the performances and result have been met with a very different reaction for each side.
For Rangers, the win has been hailed as an indicator of how much they have improved under Warburton's rule and as proof that they can return to challenging for honours in the top flight next season.
For Celtic and Deila, however, the loss is a damning indictment of their struggles to establish dominance in the Gers' absence this season, and with the Norwegian boss under pressure even before the clash, Johnston believes his time may now be up.
Johnston told the Scottish Sun: "Rangers had a tremendous game. The way they played and possessed the ball was tremendous. Moving forward, the goals they scored — everything about them was top-notch.
"They need to go out and strengthen, maybe get as many as four or five. They need numbers. But when you get better players coming in, they'll be wonderful given Mark Warburton's style of play.
"The last 30 minutes of the game was terrific, end-to-end stuff. Rangers were by far the better team and just going on that game, Ronny Deila should go."
Johnston is right to suggest that Rangers will have some serious work to do in the summer transfer window, but after such a successful season on all fronts this term, there would seem no reason that they cannot immediately start to compete in the top flight.