Rangers 1 Celtic 0: Kevin Thomson's first goal for Rangers since signing from Hibernian 14 months ago made the difference against Celtic at Ibrox as the home side took a giant step towards the Scottish Premier League title.
There was only a minute of the first half remaining when the midfielder played a one-two with Jean-Claude Darcheville before firing past Hoops goalkeeper Artur Boruc.
The second half was frantic and evenly matched but at the final whistle Rangers had increased their lead over the champions to six points, with a game in hand.
Rangers midfielder Steven Davis insisted there would be no premature title celebrations from the Ibrox side despite the win.
"We knew it was going to be a big game and we're delighted with the performance and the result," Davis said afterwards.
Davis, on loan from Fulham since the end of January, believes Celtic will not be giving up hope of a third successive league title.
He added: "This was a big game but there are still plenty of games to come. We've got to go to their place twice. They will be two massive games.
"We'll not get carried away but we'll try to enjoy the win today. We're delighted with it."
The Northern Ireland international hailed the contribution of the Rangers rearguard as the hosts kept another clean sheet.
"I think the defence and Allan McGregor have been magnificent all season," Davis said. "Since I came here they have been outstanding."