GLASGOW, Jan 20 (Reuters) - Substitute Jean-Claude Darcheville fired a last-minute winner for Rangers as they beat Inverness Caledonian Thistle 1-0 on Sunday to go four points clear at the top of the Scottish Premier League. The French forward, who replaced Steven Naismith at the interval, tucked the ball in from 12 metres after a Steven Whittaker lob. 'We applied a little bit of pressure and I felt a goal was coming, but the more the game went on that came into doubt,' relieved Rangers manager said. 'It was a hard-fought win ... I am delighted to win as not many teams win here this season.' Rangers have 50 points from 21 games, while champions Celtic are second on 46 from 21 following their 1-0 home win over Kilmarnock on Saturday. Rangers keeper Allan McGregor denied Thistle's Finnish striker Markus Paatelainen in the 25th minute by racing quickly from his line to block his seven-metre shot with his legs. Three minutes later, Thistle keeper Michael Fraser did well to smother a downward header from French striker Daniel Cousin from six metres and he also blocked a near-post effort from Whittaker before the break. Rangers came close in the second half when Charlie Adam hit a 20-metre shot narrowly over the top following a clearance by McGregor in the 62nd minute. Adam then hit a low, angled shot which appeared to be touched in by Cousin, only to have the effort ruled out for offside although television pictures showed the Frenchman was level with a defender. Adam was out of luck again when he rattled the crossbar in the 77th minute but just as the match looked destined to end in a goalless draw, Darcheville turned a low shot into the net.