Rangers recorded a fourth straight Premiership win to re-establish a seven-point lead over Aberdeen in the battle for second place.
The hosts took the lead when Martyn Waghorn’s shot was deflected in by Brad McKay at the near post.
Andy Halliday went close but Greg Tansey’s shot was tipped away for Caley and Liam Polworth missed an open goal.
Rangers toiled after the break and they needed Wes Foderingham’s save from Alex Fisher to deny Thistle an equaliser.
Victory extended Rangers’ longest Premiership winning run of the season, but Caley can count themselves unlucky not to leave Ibrox with a point.
Defeat – their eighth game without a win – left the Highlands outfit bottom of the table at Christmas on goal difference from Hamilton.
The hosts lacked the same spark which had driven them to victories over Aberdeen, Hearts and Hamilton during a flat first half.
They were grateful that Losana Doumbouya’s effort for Caley lacked the pace to beat the alert Foderingham, and a minute later, Rangers were in front.
Waghorn drove to the byline before firing a cross into the box which seemed to be aimed at no-one in particular.
But McKay was unable to get out of its path and watched in horror as the ball fired off his thigh and bounced into the net.
Halliday had Foderingham to thank when he played the ball straight to Larnell Cole in shooting territory, although the Rangers midfielder then saw a fierce 25-yarder saved by Owain Fon-Williams.