Kelechi Iheanacho was on the wrong end of a hugely controversial handball decision before Braga wrapped up a 2-0 Europa League win at Celtic Park.
Iheanacho appeared to have brought Celtic level in the 51st minute after Kasper Schmeichel made a mess of dealing with Ricardo Horta’s long-range strike in the first half.
But German referee Tobias Stieler disallowed the goal and video assistant Christian Dingert stuck with the decision, despite no handball being evident on television replays.
Iheanacho capitalised on a loose pass from a free-kick to charge down a scrambled clearance from former Celtic defender Gustaf Lagerbielke before slotting home.
The ball appeared to hit the striker’s face and there was no hint of handball in the replays that followed.
But Dingert stuck with the decision after more than two minutes of studying the footage.
Kieran Tierney and Sebastian Tounekti were denied by good goalkeeping as Celtic chased an equaliser in an open second half.
And Brendan Rodgers’ side were left with one point from their opening two matches after Gabri Martinez netted on the rebound five minutes from time.
The Celtic Fans Collective had called off a planned 29-minute silence late on Wednesday night after supporter groups accepted an invitation to meet with board members on Monday amid protests over the club’s transfer strategy and failure to qualify for the Champions League.
However, chants of “all Celtic fans against the board” and calls for chairman Peter Lawwell to quit rang out after the second goal.
Celtic had started on the front foot, with Tounekti driving a dangerous ball across the goalmouth before forcing a save.
However, there were clear signs Schmeichel was having an off night as the goalkeeper conceded possession several times before being beaten from 35 yards in the 20th minute.
Horta was not closed down quickly enough by Paulo Bernardo and his shot swerved and dipped. But it was not particularly powerful or in the corner and the static Dane appeared to be caught off guard before clawing the ball into the roof of the net.
Celtic looked rattled and needed some good defending from Liam Scales and two saves from Schmeichel to keep the score at 1-0 before the break.
Rodgers made a tactical switch at half-time, replacing Colby Donovan with Marcelo Saracchi and moving Tierney into a back three.
The hosts improved and Iheanacho took a heavy touch when presented with a good chance before being denied by the referee.
The second half was end to end. Schmeichel made a save, Scales and Tierney produced important blocks and Lagerbielke slid in to prevent Iheanacho converting Daizen Maeda’s low cross.
Braga goalkeeper Lukas Hornicek stopped Tierney’s back-post header before flying to his left to push away Tounekti’s effort after great skill from the winger.
Celtic were soon back under pressure, though, and Martinez netted from close range after Schmeichel and Scales had blocked efforts.
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