Curtis Allen twice put the Glens ahead but Crusaders levelled twice through a Gavin Whyte penalty and a late goal by former Glens player Richard Clarke.
Linfield are back in second place, Andrew Waterworth (2) and Mark Stafford scoring in a 3-0 win over Carrick.
Fra McCaffrey got both in Ballymena's 2-0 win over bottom club Portadown.
Crusaders' season has been characterised by an ability to score late goals and they repeated the feat to stretch their unbeaten home record to 27 games.
Allen converted from close-range to put the visitors ahead after 11 minutes. However, Jonny Addis' blatant foul on Jordan Owens led to Whyte levelling from the penalty spot.
Glentoran's top scorer struck again just shy of the hour mark, poking Aaron Harmon's cross under keeper Sean O'Neill.
Crusaders poured forward in search of a second equaliser but were met with a resolute Glens defence and an inspired Elliott Morris in goal.
The keeper produced a string of first-rate saves to deny the champions, most notably from a towering Owens header.
Morris was beaten though when Clarke fired a right-footed drive past him for the equaliser with just four minutes remaining.
Morris clashed with a Crusaders supporter at the final whistle after claiming he was spat on.
"I can take all the verbal abuse and name calling - I can take that all day," Morris said.
"But when someone spits at you from two yards it is hard.
"But, listen, it was a good game today and I think both teams were disappointed they did not win."
Linfield made light work of Carrick Rangers at Windsor Park with a convincing 3-0 win.
Striker Waterworth struck twice before defender Stafford wrapped up another three points for David Healy's Blues, who duly responded to Cliftonville's win over Coleraine on Friday night.
Ballymena beat Portadown 2-0 at the Showgrounds to move into fourth thanks to a quickfire double from McCaffrey.
"There were not that many clear cut chances," Ballymena captain Allan Jenkins said.
"We had a lack of quality in important areas but we regrouped at half-time and in the second half we were much better and perhaps shaded a narrow victory.
"We had been poor in the last few matches but we know we can jump back up the table."
Crusaders saw their lead at the top of the Premiership reduced to five points as they were held to a 2-2 draw at home to Glentoran.