Lee McCulloch grabbed a late goal to hand Rangers a 2-1 win at Motherwell, putting Celtic's title celebrations on ice.
A draw at Fir Park would have handed Celtic the chance clinch the SPL title at home to St Johnstone on Sunday, but they will have to wait at least another week.
Motherwell took an early lead, with Henrik Ojamaa tapping home following a surging run from Chris Humphrey. The lead did not last long as Steven Whittaker collected the ball 30 yards out and hit a swerving shot that flew into the bottom corner.
Both sides had chances in the second half. Allan McGregor made a brilliant save to deny Michael Higdon, while at the other end Kyle Lafferty had a good chance charged down.
But just as Celtic fans were starting to plan their celebration, a long throw bobbled along the six-yard box and McCulloch popped up to stab home. Rangers are now six points clear of Motherwell in the battle for second.
Dundee United moved up to fourth after strolling past bottom-club Dunfermline 3-0 at Tannadice Park.
After a goalless first half, Jon Daly broke the deadlock shortly after the restart, before Scott Robertson doubled United's lead with ten minutes remaining. And there was still time for Daly to grab his second as United went above St Johnstone in the table on goal difference .
Rudi Skacel scored twice as Hearts secured their place in the top six before the split with a 3-0 victory over fellow Scottish Cup semi-finalists Aberdeen at Tynecastle.
Defender Ryan McGowan headed in a Danny Grainger corner from close range to put Hearts in front after 27 minutes before forward Skacel netted with a trademark left-footed strike from 25 yards after 53 minutes and sealed victory with an 89th-minute third.
St Mirren won their first league fixture of 2012 at the expense of Kilmarnock at St Mirren Park. Saints striker Steven Thompson netted twice as the hosts came back from behind to record a 4-2 victory in an entertaining encounter.
Dieter van Tornhout opened the scoring for the visitors after 11 minutes before Thompson beat Cammy Bell for the equaliser 13 minutes later.
Saints midfielder Steven Thomson headed home Dougie Imrie's cross to give the hosts a 2-1 lead before Nigel Hasselbaink seized on Mohamadou Sissoko's mistake five minutes later to make it three. Thompson grabbed his second of the match when he curled a wonderful effort beyond Bell with seven minutes remaining before Dean Shiels hit a late consolation for Killie.