Dundee boss Neil McCann refused to point the finger of blame at goalkeeper Jack Hamilton – but hinted St Mirren custodian Craig Samson should have been sent off.
Hamilton gifted the Buddies their late winner in Paisley when he stepped on the ball, allowing Ryan Flynn to tee up Danny Mullen for his second goal of the day.
But the frustrated Dens manager indicated he thought Samson should have walked after 58 minutes for bringing down Jean Mendy in the box.
Referee Alan Muir, however, only flashed yellow and Samson made amends for his mistake by saving Sofien Moussa’s penalty as the Ladbrokes Championship winners went on to mark their top-flight return with a 2-1 win.
McCann said: “It was just a bad decision from Jack. We all make mistakes. We’re trying to encourage him to play but at the moment in time it was not the right thing.
“I think his mind maybe just got a bit clouded. He took the wrong decision and we paid a heavy penalty.
“Of course he is disappointed. He’s come in and apologised to the boys.
“But I’m not going to go through him as I thought he made some good stops in the first half. He’s made a mistake which he knows. I’m not going to go in and state the obvious.
“We should be ahead before that though. We had a gilt-edged opportunity from the penalty spot. It was a good save from big Craig. Whether he should still have been on the field, I have my thoughts on that.
“I don’t have a problem with the new rule because the triple punishment can be harsh at times, but it’s whether he makes a genuine attempt to play the ball.
“The keepers hedge their bet. If they’re clever enough they go low, but he’s not getting the ball. He’s never getting the ball. So there’s no genuine attempt for me. I think it’s passed him before he’s dived, so therefore he’s cleaning out the player.
“But he stays on the field and makes a good stop, which Moussa is unhappy about.”
Saints chairman Gordon Scott unfurled their Championship flag ahead of kick-off and the party atmosphere was taken up another notch as Mullen headed home after nine minutes.
Elton Ngwatala responded four minutes later as he rifled in off the post but after surviving a number of scares, Saints pounced on Hamilton’s late gaffe to snatch their first opening-day Premiership win since 2006.
Buddies boss Alan Stubbs said: “It was a great way to celebrate the title flag being unfurled but it was far from a perfect display.
“There was a period when it would have been easy to go under but they didn’t and we benefited from Jack’s mistake at our winner.
“I feel for him but we will take any luck which goes our way.”
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