Nicolas Kuhn scored his first goal for Celtic but pre-match dissent from the visiting supporters at Pittodrie was amplified after a 1-1 draw at managerless Aberdeen on Saturday.
Rangers moved to within three points of the Scottish champions, with a game in hand to come, after they beat Livingston 3-0 at Ibrox.
A banner reading "on your heads be it" aimed at the Celtic board was held up in the away support after what fans perceived as poor business in the January transfer window.
Celtic's latest accounts showed £72 million in the bank, but they spent just over £2 million on Kuhn in January, also bringing in Adam Idah from Norwich on loan.
The visitors dominated the first half and had a goal ruled out by a VAR intervention for offside against Luis Palma when he turned in after just six minutes.
Aberdeen sacked Barry Robson in midweek but caretaker boss Peter Leven had something to cheer when Bojan Miovski curled home the opening goal with their first shot on 50 minutes.
German winger Kuhn quickly levelled when his deflected shot found the far corner after a pass from Idah.
But Celtic failed to find a winner, which is certain to increase the scrutiny of the club's board and manager Brendan Rodgers.
Rodgers' men held an eight-point lead in November but could go into Wednesday's clash at Hibernian in second should Rangers beat Aberdeen at home by three goals.
"There's lots of games to go we have to sort it out on the field, that's the reality of it," said Rodgers.
"It's my job as the manager to ensure we get up to the levels we need to consistently."
Fabio Silva scored his first Rangers goal as Philippe Clement's men enjoyed a comfortable afternoon.
The Portuguese striker, who arrived on loan from Wolves last month, ended bottom-of-the-table Livi's resistance in the 40th minute.
Rabbi Matondo's deflected effort quickly doubled Rangers' lead before halftime.
Todd Cantwell added a third after the break as Rangers made it seven consecutive home wins in the league.
Hearts extended their cushion in third as Lawrence Shankland scored twice in a 3-2 win at Dundee.
Fourth-placed Kilmarnock were held 1-1 at Motherwell.
Hibs boss Nick Montgomery could be the next manager for the chop in the Scottish top flight after his side were beaten 3-0 at home by St Mirren.
St Johnstone pulled clear of the relegation zone with a 1-0 win at second-bottom Ross County.