Shiels has been linked with a move away from Ibrox, with boss McCoist and chief executive Graham Wallace looking to trim back on the club's expenditure.
But the 28-year-old showed his worth by netting either side of the interval to secure a comfortable 2-0 win against East Fife.
The inclusion of Shiels was one of two changes made by McCoist who was without Arnold Peralta through suspension and the likes of injured David Templeton and Lewis MacLeod.
Those in attendance observed a minute's silence for former Rangers player Ian Redford - a team-mate of McCoist - who died on Friday.
An energetic Rangers start to the game resulted in an early bombardment of the East Fife goal with Andy Little shooting wide as early as the first minute.
Two minutes later, Fraser Aird was denied by a defensive block, before Little was denied off the line by Fifers man Gary Thom.
From the resulting Aird corner-kick, the ball trickled through to Shiels who made an instant impact, lashing home with his right foot with the help of a deflection.
In a relentless foray forward after the opening goal, Little was booked by referee Don Robertson for simulation inside the penalty box.
The Scots-Canadian winger Aird brought his usual enthusiasm to the game and he was denied after 22 minutes by a last-ditch block from Thom.
But after weathering the early storm, Gary Naysmith's side settled and became more assured in possession in midfield with former Rangers man Stephen Hughes returning to his old stomping ground.
The Fifers created an excellent opportunity after 25 minutes with Bilel Mohsni stretching out a long leg to block Liam Buchanan, while winger Ross Brown found the side-netting with the rebounding ball.
Apart from Mohsni's free header in the six-yard box, East Fife could feel unlucky not to be level, as Rangers dropped down the gears and several bursts forward broke down.
Brown was handed his second shot at Cammy Bell's goal inside a few minutes and he carelessly dragged the ball wide of the Rangers goalkeeper's post after a fortuitous break of possession.
McCoist's side did end the half on the front foot with top-scorer Jon Daly blowing a one-on-one opportunity with Fifers goalkeeper Greg Paterson after 43 minutes.
The Irishman controlled inside the box with a few touches but lost his balance at the crucial moment, as the ball hit the side-netting.
The biggest cheer of the afternoon arrived at the half-time interval with both sets of supporters showing their support for Fernando Ricksen who is battling motor neurone disease.
East Fife started the second period brightly with Rangers skipper Lee McCulloch going very close to turning Hughes' cross into his own net.
After 54 minutes, Buchanan struck wide for the Fifers and on the hour mark, Bell produced a top-drawer save to prevent Gary Fisher from scoring a deserved leveller for the away side.
As the home fans grew restless - and as McCoist prepared a substitution - Rangers worked a neat second goal after 63 minutes as Little combined intelligently with Shiels who blasted high into the net.
But with the second - and crucial - goal behind them, the Ibrox side were on easy street, as East Fife rarely threatened in the final half hour.
Rangers maintain their unbeaten league record this season after 20 matches in Scotland's third-tier.