Ryan Naderi's strike gave Rangers their second win against Celtic in seven days to move within two points of their Old Firm rivals at the top of the Scottish Premiership.
Martin O'Neill had insisted Celtic's confidence was not "rock bottom" after their League Cup defeat at Ibrox was followed by a loss to Ferencváros in the Europa League. But, in front of 60,000 of their own supporters, it certainly took another huge dent.
After Auston Trusty's opener was ruled out for offside, Rangers took the lead. Ryan Naderi fired in on the rebound after Viljami Sinisalo denied Minsu Kim as the cheers turned to jeers at Parkhead.
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Kieran Tierney hit the woodwork as the champions looked to respond, with Djedi Gassama then doing the same at the other end.
Celtic's first chance on target did not come until after half-time, but Ivor Pandur produced a huge save to keep Colby Donovan's header out.
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Rangers continued to push. Olwethu Makhanya volleyed past Sinisalo but VAR also ruled out his effort, this time for handball.
Celtic were booed off the pitch on the full-time whistle as Derek McInnes became the first manager since 1991 to win his first two Old Firm games.
More to follow...
The key moments from Celtic Park
6: NO GOAL FOR CELTIC! Trusty finishes well but Scales had strayed offside before heading across to his fellow centre-back.
27: RANGERS SHOT ON TARGET! Neil with it as his shot deflects into the arms of Sinisalo.
28: AND ANOTHER ONE! Naderi with a header this time, but again it's an easy save for Sinisalo.
30: TIERNEY HITS THE BAR! Nygren works the ball out to Tierney, who hammers a shot which beats Pandur but not the bar.
33: GOAL RANGERS! Kim is denied by Sinasalo, but he pushes it out for Naderi to rebound home.
36: RANGERS NEARLY 2-0 UP! Gassama hits the woodwork.
42: CELTIC DANGER! Duran gets inside the box to clip a cross into the box but Rangers clear.
46: BIG SAVE TO DENY CELTIC! Celtic have their first shot on target immediately after half-time, but Pandur is equal to Donovan's header at the back post.
53: RANGERS CHANCES! The first one sees Sinasalo palm out Penrice's low shot into the danger area, then Naderi can't rebound home.
54: CLOSE! The visitors believe they can double their lead here as Kim has a shot towards the bottom corner, which whistles just wide of the post.
64: HUGE RANGERS CHANCE! Carter-Vickers scrambles Naderi's ball wide at the back-post.
74: NO GOAL FOR RANGERS! Makhanya's volleyed effort silences Celtic Park, but he handled it first.
79: RANGERS CHANCE! The visitors can't kill this off! Curtis has a shot from an angle which is straight at Sinasalo.
82: CELTIC DANGER! Hassan delivers a ball from the right but it's just overhit for the head of Hogh.
86: FORREST SHOT DEFLECTED OVER! Forrest has a shot from close range which is well deflected over.
What the result means and next fixtures...
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