THE very real prospect of Celtic completing what would be only the fourth domestic treble in their 129 year history on the 50th anniversary of their historic European Cup triumph has been exciting their supporters for some time now.

The possibility of St. Mirren repeating their 1987 Scottish Cup triumph 30 years on, however, isn’t one which many, or indeed any, of the Paisley club’s long-suffering fans will have considered. Just surviving in the second tier has been the limit of their ambitions during what has been other truly wretched campaign.

Yet, for nearly an hour at Parkhead yesterday the 2,000 or so Buddies diehards who had made the short journey through to Glasgow to watch their side in action in the quarter-final of the William Hill-sponsored competition will have dared to dream. With some justification too.

Read more: Brendan Rodgers: St. Mirren are the best Scottish side Celtic have faced - they could survive in the Premiership

Jack Ross’s side took the lead in the 13th minute when Harry Davis, the Crewe centre half who is on loan at St. Mirren until the end of the season, rounded off a delightful move. They could easily have forged further in front in the second half.

Stephen Mallan looked on in disbelief as his free-kick was turned onto the underside of the Celtic crossbar by Moussa Dembele and somehow stayed out. Had it bounced over the line and not in front of it then the final outcome could have been very different.

After surviving that scare, Celtic were immense. Brendan Rodgers had replaced the industrious but ineffectual Gary Mackay-Steven with Patrick Roberts at the start of the second half and then taken off the equally anonymous Nir Bitton and put on Leigh Griffiths. His changes certainly had the desired impact.

Mikael Lustig levelled when he nodded a Roberts free-kick in, Scott Sinclair whipped a spectacular individual effort into the top corner, Dembele atoned for his earlier error with a close-range strike and Griffiths scored his first goal since returning from injury.

"The game needed the substitutions,” said Rodgers afterwards. “I know what their qualities are and what they can bring to the game. Sometimes we use them, sometimes we don't. But what it shows is that I have a very strong squad capable of creating chances and defending very well.”

It is impossible to say the Scottish champions, who are now undefeated domestically in 33 consecutive games, wouldn’t have done the same even if they had conceded again. They certainly responded emphatically to falling behind to both Motherwell and St. Johnstone this season.

Read more: Brendan Rodgers: St. Mirren are the best Scottish side Celtic have faced - they could survive in the Premiership

Yet, neither Rodgers nor Lustig were being in the slightest bit condescending when they praised the quality of their opponents’ display. Top flight teams have failed to perform with such confidence and skill at Celtic Park this season.

There may be no repeat of their fondly-remembered Scottish Cup triumph this term. But if St. Mirren, deserved 2-0 winners against second tier leaders Hibs at home on Wednesday evening, can maintain this sort of sparkling form then they will avoid relegation in the final weeks of what has been a difficult campaign.

“There aren’t many teams who come up here and are really disciplined and actually play really good football,” said Lustig. “It is really strange that they are at the bottom of the Championship. They played a really good game. If they had got to 2-0 it would have been tough for us.”

Celtic are now just two games away from completing what would only be the fourth domestic trebles in their existence. They won the League Cup, Scottish league title and Scottish Cup in 1967, 1969 and 2001. It is nigh on impossible to see anyone preventing them from emulating their predecessors.

“We have a big chance,” said Lustig. “Yes, we have two tough games left. We have been to Hampden this year and played really good football. Hopefully we can continue that.”

Still, the match yesterday was a stark reminder that upsets can and do happen. "It showed how difficult it is to win a game of football,” said Rodgers. “It showed that if you fall below the standards expected of you and don't have the characteristics in your squad to turn it up and go again, it can be very difficult.”

Celtic’s attention will return to the league now and to the fourth meeting of the season with their near neighbours Rangers in what is now also a dress rehearsal for their cup semi-final.

Read more: Brendan Rodgers: St. Mirren are the best Scottish side Celtic have faced - they could survive in the Premiership

The majority of the starters are obvious. But who plays in central midfield alongside Scott Brown, behind lone striker Dembele and out wide is unclear. But Roberts and Griffiths will have done their cause no harm whatsoever with their contributions yesterday.

Eboue Kouassi, the Ivorian midfielder who joined Celtic in a £2.8 million transfer from Russian club Krasnodar during the January transfer window, made his debut yesterday, but it is unlikely he will feature.

The same is true of Mackay-Steven. Rodgers damned the winger with faint praise when he described his efforts afterwards.

"Bless him, young Gary worked very, very hard," he said. "But he could have been playing for the next 10 hours. I thanked him for working hard, but said it was not his day."

It wasn't to be St. Mirren's day either. But Jack Ross's players can be proud of putting up more of a fight against Celtic at Parkhead than many Premiership clubs and can take confidence into their remaining league matches as a result.