Steven Gerrard's first taste of the Glasgow derby ended in defeat.
Oliver Ntcham's second-half strike proved enough to give Celtic three points and move the Hoops into second place in the Scottish Premiership table.
For Rangers, though, it was the first defeat under Gerrard and one which left their manager very unhappy.
The former Liverpool captain felt as though his team should have been awarded a free-kick in the build-up to Celtic's goal.
"The referee cost us," he said, referring to what he felt was a foul on Ryan Jack by Tom Rogic.
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Replays seem to confirm that Jack, in fact, slipped. Gerrard, however, said post-match that he heard the fourth official tell the referee it was a 'foul.'
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Defeat condemns Rangers to their worst start to a league season in 29 years, with just one win – and five points – from four matches.
Gerrard set his team up to defend and Celtic duly dominated, tactics which have attracted criticism from many on social media.
The 38-year-old didn't share that assessment, saying he felt his players 'grew into the game.'
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"Second half we were a lot better," Gerrard said.
"The first half, we didn't make enough passes even though our shape was OK but I feel we've been done by a refereeing decision. For me, it was a blatant foul and if we get that, we could have come away with a point which would have been a satisfactory result."
Celtic boss Brendan Rodgers saw things differently, telling reporters that his side dominated the game from start to finish.
"We were the very dominant team for start to finish," the former Liverpool boss said.
"Defensively, we were strong, we pressed the game well and had the courage and quality to play. Steven [Gerrard] has done well getting them organised so we had to be patience. The scoreline doesn't really reflect our dominance.
"We showed a calmness to play round them and play through them. Our only complaint is not scoring one or two more. It's an important three points for us. There's a lot more to come from this squad."
