Amid a celebratory trophy-day atmosphere fringe player Johnston fired in the opener with less than two minutes played but that was cancelled out in the 17th minute by Hearts winger Jake Mulraney.

Neil Lennon replaced Oliver Burke with highly-rated 16-year-old debutant attacker Karamoko Dembele for the start of the second half and he showed plenty of promise, but with six minutes remaining it was Johnston who stepped up with a terrific run and drive to seal the win.

Two unusual but not unexpected line-ups were revealed on the team sheet with the Hoops showing seven changes from last week's 2-0 defeat at Rangers.

Skipper Scott Brown, Mikael Lustig, Odsonne Edouard, Tom Rogic, Jonny Hayes, Kieran Tierney and James Forrest were all left out, mostly with niggles, with Callum McGregor and Jozo Simunovic on the bench.

Youngster Anthony Ralston and Ewan Henderson and Jeremy Toljan and Nir Bitton were given rare starts.

Craig Levein made nine changes as he gave 16-year-old left-back Aaron Hickey his first start.

Skipper Christophe Berra, Bobby Burns, Steven MacLean and Harry Cochrane were rested with the Jambos boss hoping Peter Haring, Arnaud Djoum and burly striker Uche Ikpeazu are fit for Hampden.

The champions were given a much-appreciated guard of honour by Hearts before the game at the request of the visitors.

There was then a minute's applause before the game in tribute to Lisbon Lion Stevie Chalmers who died recently.

Winger Johnston got the home side off to a great start when he worked a one-two with Henderson and slammed the ball past Zdenek Zlamal from eight yards out.

Mulraney screwed a shot wide a minute later at the other end but was much more accurate with his leveller, after Hoops keeper Scott Bain was slack with a pass.

Sean Clare took possession and rolled the ball to the former Inverness player who curled the ball past the back-tracking Bain and into the top corner.

Zlamal made a terrific save from a Johnston drive early in the second half before Dembele flashed a 25-yard drive just wide, drawing huge applause from the Hoops fans before having another effort saved by the Tynecastle keeper.

Celtic, captained by Scott Sinclair, piled on the pressure and there was a penalty claim in the 80th minute when defender Kristoffer Ajer's drive following a long run was blocked by Conor Shaughnessy but referee Craig Thomson was unimpressed.

However, the home fans were impressed when Johnston played a one-two with substitute McGregor, on for Henderson, and drove towards the Jambos goal before firing low past Zlamal and in off the post from the edge of the box for the winner.

Part two of the contest will take place at Hampden next week where the stakes will be much higher.