Dundee United looked to have done enough for the three points, but the midfielder took matters into his own hands two minutes into injury-time to ride two challenges before cracking home the equaliser.
It was a pulsating contest but the point gained by United leaves Celtic clear at the top of the SPL.
The home side started impressively and Lukasz Zaluska was called into action early to turn a Steven Davis shot past his post for a corner.
Just when United looked to have settled, Rangers moved in front after 11 minutes when Davis worked himself an opening at the edge of the area and sent a low shot past Zaluska.
Dundee United looked to hit back immediately and Scott Robertson had a chance after Rangers failed to clear a free-kick but he sent his shot over the top.
Craig Levein's side did not have long to wait for the equaliser as Francisco Sandaza produced a wonderful finish to leave Allan McGregor with no chance after some slick passing by United.
Kris Boyd had the ball in the net at the other end moments later but the effort was chalked off for offside.
United went in front after 27 minutes when Paul Dixon cut the ball back for Robertson and, when McGregor failed to hold his shot, Sandaza reacted swiftly to net his second goal.
Lee Wilkie then had a chance after a flick on from Darren Dods but his finish was careless and he sent his shot wide.
Kenny Miller then beat the United offside trap but his shot across the face of the goal failed to pick out Boyd at the far post.
But Rangers were level nine minutes from the break when a great pass from Nacho Novo set up Sasa Papac and he beat Zaluska with a well-placed left-foot shot for his first goal for the club.
The frantic pattern continued in the second half and Zaluska made a fine save to divert a Boyd shot past his post.
United stunned Rangers again after 59 minutes when they failed to deal with a long throw-in and it broke kindly for Robertson to provide a precise finish.
Zaluska produced another decent save from Boyd after Thomson had created the opening for Rangers.
United had to sit in to absorb some late Rangers pressure but the home side did not help themselves with some indifferent finishing.
Just when it looked as if United had weathered the storm, Thomson produced his dramatic equalising goal.