He calls the referee across to the screen. Here we go...

Sterling shows great pace to get to the spinning ball first. It is close, but it looks clear that Sterling gets to the ball first.

Matthew MacDermid says... Penalty to Rangers!

Dujon Sterling goes down in the box under the challenge of Andy Considine. That must be a penalty!

Not given - yet! Matthew MacDermid looked to his assistant to help him out there, and he got nothing back.

I'm sure the VAR Greg Aitken will have a look at this.

St Johnstone go down the pitch and win a free kick on the left hand side. Matt Smith is over it. He could cross, or he could roll it to Graham Carey.

He puts it in a dangerous area and John Lundstram's defensive header goes just over the bar. That was close.

The resulting corner is headed away and Ryan McGowan takes a swipe out of Connor Goldson as he tries to hit a shot at goal. Unlucky for the big Aussie.

Dan Phillips goes into Matthew MacDermid's book as he trips Tom Lawrence on the edge of the area. This is a perfect position for either James Tavernier or Borna Barisic.

It's Barisic who curls, but it's comfortable for the quick-moving Dimitar Mitov.

More Rangers changes. Cyriel Dessers and Ross McCausland come on, with Fabio Silva and Oscar Cortes off.

They've been a little quiet this afternoon.

Martin Dowden
BBC Sport Scotland at McDiarmid Park

St Johnstone are still competing here although Philippe Clement will feel they should have that second with Dujon Sterling missing that glaring chance.

Craig Levein is clearly trying to exert more pressure in the final third. It's not paying off in chances but is at least giving Rangers something to consider.

Dujon Sterling is played in by Fabio Silva but he can't get the ball out of his feet and he's dispossessed about eight yards from goal.

This has been a far more open half.

Callum Davidson
Former St Johnstone manager on BBC Sportsound

St Johnstone miss Drey Wright. He's been out for three or four months, and they haven't filled it.

He's the one to get them forward and create.

Now, there's a surprising change. Todd Cantwell is off, with Tom Lawrence coming on.

A like for like swap, but Cantwell has probably been Rangers' most creative player. The former Norwich man is held in an embrace by Philippe Clement, who whispers in his ear.

A reassuring nod of the head from Cantwell.

Huge change! Todd Cantwell clips in a brilliant cross from the left and Dujon Sterling glances a header just wide from right in front of the goal.

Any sort of meaningful contact, and that would have been on target. Has to do better.

Fabio Silva is almost clear through in the box as he loops the ball over Liam Gordon's ahead, but the ball doesn't fall quick enough for the Portuguese striker and Gordon can get back.

They win a free-kick seconds later as James Tavernier is chopped down. Tavernier clips in, but it's headed away.

Appeal for a St Johnstone penalty there. Connor Smith is on the end of a Saints through ball, but he goes down under the challenge of James Tavernier.

Callum Davidson on co-comms says 'no', which tells you it's soft.

The second half begins!

Scott Wright is hooked. Dujon Sterling is on. He seems to be playing on the wing.

St Johnstone wing-back David Keltjens is also off, after being booked. Benjamin Kimpioka is on - that definitely will be a change of Saints shape, he's a striker.

Rangers make a quick start! Sterling squares for Fabio Silva who volleys first time and Dimitar Mitov has to make a great save.

Let's bring you some stats, that might give us a clue as to how the second half will play out...

• St. Johnstone have failed to score a first-half goal in 19 of their 26 games, only Ross County (21) and Livingston (20) have failed to score more often in the Scottish Premiership this season.

• Rangers have a record of W18, D0, L0 when leading at half-time in the Scottish Premiership this season.

• Rangers are unbeaten in their last 84 Scottish Premiership matches when leading at half-time (W79, D5) dating back to 12th February 2020 against Kilmarnock (L1-2).

• Rangers have stopped the opposition from scoring a first-half goal in 18 of their 26 games, only Hearts (20) and Celtic (22) have done this more often in the Scottish Premiership this season.

Image source, SNS

Martin Dowden
BBC Sport Scotland at McDiarmid Park

Our BBC pundit Michael Stewart never shirks a controversial moment but he surely has gone too far here.

What on earth has he brought for his half-time snack when these glorious pies are on offer?

Lack of judgement at such a crucial moment.

Image source, BBC Sport

Lee McCulloch
Former Rangers captain on BBC Sportsound

The [Rangers] threat has been out wide. After the goal, Rangers were in the ascendancy and didn't want half-time to come. That came after they switched the wingers over.

Tactically, it's been a good game. Quality wise, it hasn't. It's been scrappy, the pitch has a lot to do with that. The keepers have had almost nothing to do.

St Johnstone can't be too downhearted, they defended well in general. Craig Levein will want to keep it at 1-0 and then put pressure on the goal, but not right away.

Callum Davidson
Former St Johnstone manager on BBC Sportsound

I quite enjoyed it. I liked seeing Rangers' thought process, how to break St Johnstone down and make spaces.

For the first 30 minutes, St Johnstone kept Cantwell quiet and before the goal, they'd have been quite happy. They could have done more going forward but they limited Rangers to very few chances.

The game has opened up now, Cantwell has more space to cause problems.

Rangers are on form, confident and trying things. St Johnstone mainly did that well, they're still in the game. They need a little more support to Sidibeh up top.

Craig Levein would have been fairly happy with large swathes of that first half, as his St Johnstone side frustrated and shut out Rangers for most of it.

It was just the one moment of quality that undid them, with Mohamed Diomande lacing in from 25 yards for his first Rangers goal.

It was just as the visiting crowd was starting to get a little nervous, too.

Image source, SNS