That wasn’t how someone who failed to make the grade as a youngster at Everton and Wigan Athletic felt when replacing Chidi Nwakali after 76 minutes at Pittodrie with his side losing 1-0.
Cosgrove was understandably anxious to do well after time spent at Carlisle United, as well as on loan with unglamorous non-league teams like Barrow, Chorley and North Ferriby, but too much so as it turned out.
Eight minutes after coming on, and just after Kieran Tierney added a second, the player Derek McInnes bought from the English League Two side for £25,000 the previous month was sent off for a reckless challenge on Celtic captain Scott Brown.
Between then and Cosgrove’s first goal for the club last October some were wondering if even that fee was too much, but now the Aberdeen manager expects to spend this January’s transfer window fending off seven-figure bids for the player.
Scoring 36 goals in 50 appearances since is impressive enough, but the amazing rate of one for approximately every 85 minutes spent on the pitch this season has been truly transformational.
Not that Cosgrove’s approach to the game has changed much, only the way he focuses it nowadays as he admits: “It wasn’t a good day or a good result but you have to learn from these things and I definitely have.
“You talk about being pumped up for games and you still have to have that. If anything I’ll be even more pumped up to face them this weekend as the adrenaline will still be there.
“But being more mature and having more games under my belt now, I’ve got a different point to prove. It’s not going around and trying to make a name for myself. I’ve got the responsibility to carry the team at the top end of the pitch, score the goals, put in a good performance. The determination will still be there but it’s about channelling it in the right way.”
That’s certainly what the 22-year-old has done over the last 12 months, even allowing for another red card in the first half of Aberdeen’s 1-0 league win against Rangers at Ibrox last December.
Another positive for someone it would be easy to misjudge as just a powerful big striker is the quality as well as the quantity of the goals that he has been scoring, best illustrated at Fir Park last weekend.
Cosgrove showed terrific touch for a big man with a delicate lob at pace over Mark Gillespie for the opening goal in a comfortable 3-0 win as they reduced Motherwell’s advantage over Aberdeen to just one point.
Delighted manager McInnes, inset, was only half joking when he said the striker would have put the ball out of the stadium when he first arrived at the club and Cosgrove conceded: “Confidence has a big part to play.
“The keeper was onrushing and it was just an instinct to dink it over him but a massive part of what’s changed is playing with quality players week-in, week-out.
“Living under those standards really brings your game on. You’ve got to make quicker decisions and that definitely helps when you get into a game.”
Maintaining that prolific goals ratio at lunchtime today will be crucial for getting into the game against a Celtic side they failed to score against in five of the six meetings last season.
Cosgrove did get one from the spot but that still ended in a 4-3 defeat, although he believes regardless of the result there has already been an over reaction to last month’s 5-0 defeat against Rangers.
He added:“The success of the club in the past few years under the manager is good, but it means that as soon as there’s any kind of downturn people jump on your backs quickly.
“The feeling within the club is completely different, there’s absolutely no panic here whatsoever. We’re just working even harder on the inside trying to get the right results.”