YOU know the Steven Spielberg movie Duel in which a motorist is pursued along a dusty highway by a truck driver, forever looking nervously in his rear-view mirror as the tanker gets closer and closer?

That's how Rangers must be feeling right now.

On November 5, Ally McCoist's side defeated Dundee United 3-1 at Ibrox to move 15 points clear of Celtic who, the next day, would be facing an in-form Motherwell side above them in the table. Neil Lennon's players were toiling at that time and even the most optimistic of Celtic fans would have hesitated when asked if their team could somehow claw back that deficit and go on to win the title.

And yet claw it back they have. That yawning, seemingly insurmountable, chasm has been reduced to a solitary point and Celtic are honking the horn noisily and threatening to run Rangers off the road. Should Lennon's side prevail in Wednesday night's eagerly-anticipated Old Firm derby they will top the Clydesdale Bank Premier League for the first time this season.

That such a situation has as much to do with Rangers' growing frailties as it has with Celtic's impressively consistent recent streak. In truth, the Ibrox side have been poor for quite some time but getting away with it, doing just enough most weeks as they eked out victories against the likes of Dunfermline Athletic, Hibernian, and Inverness Caledonian Thistle.

That earned McCoist and his players praise for "digging out a result" and "winning when not playing well" but their good fortune was always going to run out. There was also a feeling that Rangers looked more comfortable away from home – where there is less emphasis on them to dominate possession – but even that claim is starting to look somewhat hollow.

If a 1-0 loss at Kilmarnock a few weeks ago was written off as a blip – and, in fairness, it was their first league defeat of the season – then there are not quite as many willing to dismiss the reverse at St Mirren as another bad day at the office.

Of course, any analysis of Saturday's result – St Mirren's first over Rangers for more than three years – cannot be undertaken without looking at the mitigating factors. Rangers actually started off well and scored early on through Lee Wallace before Lee McCulloch's red card changed the entire complexion of the match. St Mirren went on to control the remainder of the first half, scoring two well-taken goals through Aaron Mooy and Paul McGowan, the game's outstanding player, to lead going into the break.

Rangers played better in the second half – Nikica Jelavic missed a snip that would have drawn them level – before Dorin Goian's needless sending off for a second bookable offence completely killed off any prospect of a late rally.

McCoist chose to focus afterwards on the red card for McCulloch – for catching Graham Carey with a swinging arm – as the pivotal moment in the match, believing his player to be hard done to. We will never know how the game would have panned out if Rangers had kept 11 men on the park but, even the numerical imbalance cannot explain poor individual performances from the likes of Jelavic and Steven Davis, whose combined contribution was again negligible.

How McCoist must have wished Steven Naismith was on the park and not working as a media pundit in the television studio at the side of it, for without him Rangers are undoubtedly toiling.

The situation now is exactly as it was ahead of the first Old Firm game of the season back in mid-September – Rangers leading by a point – although there is little doubt the momentum is now firmly behind Celtic. Form, of course, is not the most reliable barometer whenever these two meet although McCoist – despite appearing stoic and unbowed in his post-match conference – will surely have private worries about his side's lack of creativity amid some poor recent displays.

Still, they travel to Celtic Park as league leaders and will not head across town waving a white flag. "We now have this huge game just around the corner and it's a good chance for us to rectify this result," said Wallace, whose first goal since his summer transfer from Hearts was effectively reduced to a footnote. "We now need to stand up and be counted and have the right mentality. We're still top of the league. We're not bothered by what Celtic are doing, we'll just focus on what we're going to do on the day. It didn't go to plan against St Mirren, obviously, but we can look at the second half performance where there was a lot of desire and commitment. We never gave up.

"If we can take that into the full 90 minutes against Celtic then I think we'll do alright."

The last Old Firm match was arguably Rangers' best performance of the season. How they could do with another display like that this week.