Manager Philippe Clement said Rangers "threw away 45 minutes" and "three points" at St Mirren as Caolan Boyd-Munce's stoppage-time stunner ensured the Ibrox side ended Boxing Day 12 points adrift of leaders Celtic.

In an abject first-half showing from the visitors, Jack Butland's clumsy foul on Greg Kiltie allowed Oisin Smyth to send the former England goalkeeper the wrong way from the resulting spot-kick.

The aggression, intensity and defensive shape of Stephen Robinson's men was impressive, but the half-time introductions of Nicolas Raskin and Danilo raised Rangers' level dramatically.

Brazilian striker Danilo levelled from six yards just moments after he was denied from similar range by goalkeeper Ellery Balcombe, but Clement's side could not edge themselves in front.

And they watched one point turn to zero when substitute Boyd-Munce drilled in a 93rd-minute beauty from 20 yards.

"We lose very important points because we didn't perform how we should've in the first half," Clement told BBC Scotland.

"It was below, below the level we need to play. We threw away 45 minutes and because of that we threw away three points."

After appearing to take forward strides in recent weeks, this defeat sends Rangers backwards.

The faintest of hopes of a title challenge after reducing Celtic's lead to nine points last weekend will disappear quickly.

The fact their first shot on target did not come until the 42nd minute, an effort on the spin from Hamza Igamane, tells the story of their woeful first half.

Clement's team selection will come under scrutiny, given Raskin's urgency in midfield and Danilo's danger in the box upped the ante following the interval.

The Brazilian striker's equaliser came after James Tavernier curled a free-kick just wide before Vaclav Cerny smashed the frame of the goal.

But Rangers failed to take advantage when they smelled blood from their opponents, something their city rivals seem to have no issue with.

And the Ibrox side always seem to give you a chance when games are in the balance.

That was apparent again in Paisley as Dujon Sterling was dispossessed cheaply in a dangerous area in the build-up to St Mirren's dramatic winner.

Not since December 2020 had St Mirren beaten Rangers before this victory - a 3-2 League Cup win - and you have to go back to 2011 for their previous top-flight success in this fixture.

Boy, did they have to work for it. Their aggressive approach and compact shape in the first half was key to them going into the break ahead.

They then had to suffer in the second period as Rangers earned themselves a deserved equaliser, but Robinson's side responded well and came within an inch of taking the lead when Robin Propper headed a corner off his own crossbar.

And they did not settle for a point in the closing stages, evidenced by Jonah Ayunga's determination to win the ball just before Boyd-Munce smashed in his stunner.

Robinson was bold in his decision to throw on 17-year-olds Callum Penman and Evan Mooney, who assisted the winner.

It is now three wins in a row for the Paisley side, who have fourth place in their sights.

St Mirren manager Stephen Robinson: "We have to credit the resilience of the players. We moved the ball really well first half, we pressed them really high.

"When you have a right go and move the ball quickly, you'll create chances and we responded to a setback. That's the bigger thing for me.

Rangers manager Philippe Clement: "I was angry at half time. The reaction was good and the team played how they should have in the second half.

"In the first half we didn't control the midfield. Playing like this you can't win games. It's cruel to get that goal against us, but we didn't lose the game in that situation, we lost it in the first half."