Johnstone was still 16 at the time, but the faith shown in his ability by manager Willie Waddell paid off handsomely, as Rangers claimed their first major trophy for just over four years.

Despite his heroics against Celtic, Johnstone found regular first-team outings in the number '9' jersey hard to come by, largely due to the presence of Colin Stein, Scotland's first £100,000 player, although he did score 11 goals in 16 league appearances during the 1971–72 season.

[citation needed] Johnstone soon became a regular in the starting line-up, and he picked up a Scottish Cup winners' medal in 1973 when Rangers defeated Celtic 3–2 at Hampden Park.

He scored his first, a typical header, after just 42 seconds and thus earned himself a unique place in the annals of Scottish football: the referee had actually kicked off the match early, so Johnstone had actually hit the net before the allotted 3pm kick-off time had been reached.

Johnstone was the outstanding performer in what was an exceptional Rangers side, scoring thirty-eight goals over the course of the campaign and picking up the Scottish Football Writers' Player of the Year accolade.

[citation needed] With Arsenal and Tottenham Hotspur reportedly interested in luring Rangers' top marksman to London, Johnstone submitted a transfer request in the summer of 1978.

[5] He failed to dislodge the established forward duo of Kerry Dixon and David Speedie and made just four appearances, with a month on loan to Dundee United during the 1983–84 season.