Celtic gained revenge for its Champions League exit to Cluj as Neil Lennon's side got its Europa League campaign up and running with a 2-0 win over the same opponent.
Romanian champion Cluj knocked its Scottish counterpart out in Champions League qualification, with a remarkable 4-3 victory at Celtic Park seeing it progress 5-4 on aggregate.
Cluj met its match in the form of Slavia Prague in the final play-off round, dropping into Europa League Group E, winning its opening fixture against Lazio.
Its return to Glasgow was not so triumphant, however, as Odsonne Edouard and Mohamed Elyounoussi sent Celtic to the top of the group.
Celtic, which drew 1-1 with Rennes in its first outing, was swiftly out of the blocks and Edouard marked a strong start with the opener in the 20th minute.
The former Paris Saint-Germain striker scored against Cluj in the extraordinary second leg in August and proved the bane of the visitor's defence again when he headed home Boli Bolingoli-Mbombo's cross.
Fraser Forster looked to have gifted Cluj an equaliser when he parried a free-kick straight to Mario Rondon, but Kevin Boli was in an offside position as he tucked in from his team-mate's pass.
And Elyounoussi doubled Celtic's lead just before the hour, netting his first Hoops goal with a tidy finish into the bottom-right corner.
Cluj pushed back, but Forster kept it at bay with a fine save from Ciprian Deac as Celtic got a first win of the group stage.
-Fassnacht late winner stuns Gerrard's men-
Christian Fassnacht fired a stoppage-time winner to spark wild celebrations from Young Boys as they beat Rangers 2-1 in the Europa League.
The Switzerland winger completed a comeback success that was richly deserved, with his powerful 18-yard shot adding to Roger Assale's earlier leveller.
Alfredo Morelos impressively lashed Rangers ahead shortly before the break, the Colombian's class apparent throughout.
Yet the Glasgow side was second-best for long periods in the Group G contest, played on the artificial pitch of Stade de Suisse.
Young Boys had the better early chances, with Jean-Pierre Nsame guilty of a glaring miss in the 17th minute when Fassnacht's cross was flicked into his path, only for the striker to make a muddle of a near-sitter.
Cameroonian forward Assale went closer with a deflected strike from 25 yards that arrowed barely a foot away from the top-right corner.
It was against the run of play when Rangers forged ahead in the 44th minute. Morelos rolled centre-back Cedric Zesiger and powered through before cleverly disguising his shot and firing into the left corner when goalkeeper David von Ballmoos anticipated the ball going the other way.
The Young Boys leveller came in the 50th minute, Assale prodding the ball in from close range after Ulisses Garcia drove over a powerful cross from the left.
Both sides had penalty claims waved away: Rangers after Morelos looked to be caught when chasing down a dangerous cross, and Young Boys when the ball struck the hand of Rangers defender Connor Goldson.
Gianluca Gaudino shot over for Young Boys and Nsame headed wide as the Swiss side pushed for a winning goal, having lost its opening game at Porto when Rangers beat Feyenoord.
Thursday's results, with Feyenoord beating Porto, mean all four sides are on three points from two games.
It needed a sound reaction save from Van Ballmoos to turn away a deflected Morelos strike in the 90th minute, as Rangers almost pinched the spoils.
But Young Boys would have the final say, Fassnacht cracking a left-footed shot through the weary defences of McGregor to leave Rangers, and their manager Steven Gerrard, dismayed.
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