Having booked a first front-row starting slot in more than two years, Raikkonen's sights had been set on challenging for the lead on the run down to the first chicane - but instead he nearly stalled and rapidly dropped to the back of the field.
Though he eventually fought back to finish fifth, Raikkonen admitted the poor getaway had blown an otherwise fantastic opportunity.
"I don't know exactly what happened at the start. As far as I know I did everything correctly, but the car went into the antistall and did not move at all," Raikkonen said.
"I still don't have the right explanation about what happened, but it's a really bad thing that cost us a lot today. If you start from second place and after a few seconds you're in last position it's not easy to see the positive side of the race: we wasted a big opportunity to fight at the front."
The Finn said he could still draw positives from the weekend however, adding: "Overall we had a pretty good speed all weekend so in a way we have to be happy for what we have done because here we were expecting more difficulties.
"In the end I managed to come up fifth. Obviously we were hoping for a better result in our home race in front of all our fans, but if we think that after the first hundred metres we were last it was still a good result. Today I was positively surprised that we could get through some cars that are very fast on the straights, this shows that we are doing the right things, pushing the car in the right direction and improving in all areas."
Raikkonen has scored just one podium for Ferrari since returning to the team ahead of the 2014 campaign, in Bahrain earlier this year. Sebastian Vettel, who was second at Monza, has claimed eight in his maiden season with the Scuderia.