Rangers reduced the gap at the top of the Scottish Premier League on Sunday with a 4-0 win over St Johnstone as Celtic's shock 2-0 defeat to Motherwell ended their 17-match unbeaten run.
Nikica Jelavic's fiercely drilled shot gave Rangers the lead in the fifth minute and, after missing a host of chances with his feet, Kyle Lafferty headed home a second just before the break.
St Johnstone enjoyed the bulk of possession in the second-half but it was Rangers who added to their score when Sasa Papac scored a rare goal in the 81st minute and Jelavic boosted their goal difference with a strike in injury time.
At Fir Park, Celtic failed to build on last weekend's 3-0 Old Firm derby win when goals from John Sutton at the start of either half earned Motherwell all three points as the Hoops lost for the first time since November.
The results mean the league leaders have a five point lead over Rangers, who have two games in hand, as the sides prepare to meet in Wednesday's Scottish Cup fifth round replay at Celtic Park.
At Ibrox, captain David Weir, who had a bout of food poisoning before Rangers' Europa League tie against Sporting Lisbon, dropped to the bench while David Healy was handed his first start.
Boosted by the news their title rivals had lost at Fir Park Rangers were quick to take the lead in the fifth minute.
Jelavic was first to react when Maurice Edu's shot was blocked by a Saints defender in the box and the Croatian drilled his shot past Peter Enckelman for his ninth of the season.
On the half hour mark Lafferty was sent clear by Steven Davis but with time and space he lifted his shot high over the bar after cutting in from the left. The same two combined minutes later when Lafferty beat the offside trap to latch on to an excellent through ball but this time Enckelman saved as the forward attempted to place his strike into the bottom corner.
However Lafferty finally got a goal four minutes before the break when he rose to head in substitute Gregg Wylde's corner in from close range.
St Johnstone had rarely threatened but Allan McGregor had to be alert to tip a superb strike from Jody Morris round the corner on the stroke of half-time. Saints began to enjoy more possession in the second-half and Liam Craig sent a looping shot straight to McGregor before Murray Davidson fired into the side netting.
Jelavic grazed the bar with a fierce free-kick before he set up Papac to make it 3-0 in the 81st minute. The Croatian striker backheeled the ball into the Bosnian defender's path and he raced on to slot low under Enckelman from eight yards.
There was still time for Jelavic to pounce in stoppage time to send an angled shot past the despairing keeper after good work from Wylde down the wing.
At Fir Park, Motherwell got off to a perfect start when Sutton took advantage of a mistake from Charlie Mulgrew to round Fraser Forster and slot home in the second minute.
Minutes after the break Shaun Hutchinson rattled the crossbar with a powerful header before referee pointed to the spot when Keith Lasley was tripped by Emilio Izaguirre and Sutton stepped up to fire the penalty into the top corner.
Darren Randolph saved well from Scott Brown and Kris Commons as Well held on for a deserved win.