The first - Durnan notices Robson losing his man and attempts to go to help but in turn leaves his own man. Durnan slips in the box and takes himself out of the game (Should be an automatic fine for not having correct footwear IMO. Ridiculous the amount of players we have that slip each week.) 

We lose 2 headers in less than 5 seconds and concede. Yep young robson loses his man but Durnan should never be leaving his own man IMO. He's never scoring from there and even if he connects with the header, you can attack the ball and clear.. Because of this, everyone has to react within a second and change the man they mark. DIllon moves onto Sutton (who should be Durnans man) and the boy Dillon's marking is then free to score. 

2nd - Bell at fault, 100%. 

3rd - Its actually a good move from St.mirren. hit byline and ball across the box.(if only we knew how to do that eh) Questions as to marking though. Edge on his own, Durnan on one man and Dillon the next but this leaves a boy on his own at the back post. Poor organisation. They had 15seconds from Saints getting the ball to the ball hitting the next. Someones got to take leadership there, be aware of the danger and know to pass a man on within that time. It didn't need 3 boys going to their number 11. 

Alarming that we seem to have lost the basic ability on how to defend.