Last updated on .From the section Scottish League Cup

Leigh Griffiths' goal was his third in six days

Holders Celtic edged into the semi-finals of the Scottish League Cup as Leigh Griffiths' 83rd-minute goal earned a nervy win over St Johnstone.

Brendan Rodgers' side are enduring their worst start to a term since 1998 and toiled for chunks of this match.

However, Griffiths was their saviour for the second time in six days when he turned in from six yards.

Celtic face Hearts in the last four as Rodgers aims for his seventh trophy in seven attempts since taking charge.

The Scottish champions finished with 10 men after Dedryck Boyata was shown a red card for foul and abusive language, while fellow centre-back Kristoffer Ajer limped off with what appeared to be a hamstring injury.

Confidence lacking, but reward wasn't

Rodgers has spoken at length about confidence in the past few weeks - he knows it has been in short supply for a group of players who had endless amounts of the stuff over the past couple of years.

He mentioned it again before this game and once again it was in short supply at key times.

The first half was worryingly familiar for the Celtic fans huddled into both stands behind the goals - lots of side-to-side football and a head-scratching inability to break down a very organised St Johnstone.

It took a full half an hour for the visitors to create a chance and Griffiths should have scored from it. He rose to meet an excellent Odsonne Edouard cross but could only head into the feet of Zander Clark.

Another player usually bursting with confidence squandered an even better chance at the end of the first half. Callum McGregor skipped through on goal from an Olivier Ntcham through ball but the usually dependable midfielder could only fire wide.

After the break, Clark tipped a McGregor toe poke around a post before pulling off an acrobatic save from a fierce Ntcham shot moments later. Suddenly the away support started to make some noise as their side started to turn the screw.

The tempo was up and the swagger was back as Clark was once again forced to save, this time from a long range McGregor strike that was looked destined for the top corner.

Saints remain focused though and they had to. Griffiths broke free and once again should have scored, Clark again saved with his feet.

But he was not to be denied. Just like against Rosenborg in the Europa League last Thursday. James Forrest's header was deflected inside the box but when it dropped to Griffiths, he fired low into the net. It was well deserved.

Dedryck Boyata was shown a red card for foul and abusive language in stoppage time

'Relief all round for Celtic' - analysis

Celtic have so often in recent weeks stumbled against well drilled, determined sides. St Johnstone certainly fall into that category but eventually succumbed to the pressure. What might that do psychologically for the holders?

The second-half swagger witnessed in Perth must be taken into the rest of the season, but battling through when extra time was looming may just provide the platform to do just that.

Rodgers says hard work and belief will see them through their mini slump. The trophy that has kick-started two trebles was at stake against St Johnstone and his side fought for it.

Now they must regroup and fight for the rest. Relief all round for Celtic and something to smile about at last.