Rangers retained their seven-point lead in the Scottish Premier League after a controversial backs-to-the-wall draw against second-top city rivals Celtic.

Celtic were left angered when Marc-Antoine Fortune had a goal chopped off for a foul on keeper Allan McGregor.

And Rangers' Kyle Lafferty was fortunate not to be sent off for a lunging challenge on Andreas Hinkel.

Scott McDonald headed Celtic into a deserved lead after 79 minutes, but Lee McCulloch matched that seconds later.

It had been Rangers' first effort on target but secured a draw that will leave the blue half of Glasgow the happier, retaining a cushion over a Celtic side who have a game in hand.

Celtic manager Tony Mowbray had sprung a surprise ahead of kick-off by dropping striker McDonald and starting Fortune up front along with Georgios Samaras.

Stephen McManus was the man to lose out in central defence following the return from suspension of Gary Caldwell.

Novo was forced off after 11 minutes at Celtic Park

While Mowbray obviously thought those changes strengthened his side, Rangers counterpart Walter Smith's changes were required to cover for two of his top performers of recent weeks.

Rangers manager Walter Smith showed faith in 18-year-old Danny Wilson, who started in central defence in place of Madjid Bougherra, who had joined Algeria's African Cup of Nations squad.

Steven Whittaker came into midfield in the absence of the suspended Kenny Miller, with Lafferty moving up front to partner Kris Boyd.

Re-jigged Rangers started on the front foot, but Celtic's defence stood firm as the visitors played pinball with a series of attempted efforts that were blocked outside the penalty box.

Rangers' hopes suffered a blow after 11 minutes, when Nacho Novo picked up an injury and was replaced with the more defensively-minded Maurice Edu.

And, as the game settled, it was the home side who were controlling possession, with the Rangers defence increasingly stretched and their challenges becoming increasingly desperate.

It seemed only a matter of time before Celtic made the breakthrough and it looked like they had done just that after 19 minutes when Fortune headed home from five yards.

However, referee Steve Conroy ruled that the striker had led with the arm as he challenged McGregor to a miss-hit McGeady volley that flew high into the air.

Conroy appeared to have got that call right despite the resulting anger from the home support, but he was too lenient 11 minutes later when only producing a yellow card when Lafferty lunged dangerously, studs-first into the shins of Andreas Hinkel.

Celtic's speed and movement was a delight to watch, but Rangers' doggedness was denying them threats on goal until a fine Hinkel cross was met by the head of Barry Robson and looped from 15 yards off the face of the crossbar.

Samaras ought to have given Celtic the lead two minutes before half-time, breaking through the challenge of Wilson but steering his drive from the edge of the box wide of the far post.

The Greek striker and McGeady both squandered chances early in the second half despite Rangers showing more attacking intention.

Fortune pounced on an Edu mistake to tee up McGeady in the clear on the edge of the box, but the winger fired high over the crossbar.

A 16-yard snap shot on the turn from Celtic substitute McDonald almost squirmed under McGregor.

However, the Australian striker did make the breakthrough after 79 minutes, stealing in behind his marker to head home from five yards after a cross from McGeady, who had teased his way past two defenders.

The lead only lasted a two minutes, McCulloch rising above Caldwell 10 yards out to powerfully head home a Steven Davis corner.

McGregor prevented Celtic retaking the lead after 84 minutes, turning a curling 20-yard drive from Samaras brilliantly over the crossbar with his outstretched hand.