"I'm disappointed because I was so close to winning my first race for the team," he said. "As a team we all try so hard to be the best but nobody is perfect."
The Colombian was excluded after he left the pit lane under a red light, because the safety car was going past with the field behind, at the end of his second pitstop, but his problems had started before that.
Montoya had already recovered from a mistake after his first pitstop when he came out in second place ahead of Renault's championship leader only to run wide.
When both Alonso and Italian team mate Giancarlo Fisichella then retired, Montoya led ahead of Finland's Kimi Raikkonen -- who was wrestling with a steering problem -- for 10 laps until it all went wrong on the 49th of the 70 laps.
ONE-TWO
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"So we slowed the cars down, which means that you have discussion with the drivers, and Juan Pablo needed to be reassured that if he dropped his pace it was not going to cost him his race win.
"Of course we had to convince Kimi not to overdrive the car with his problem.
"There was some tension on the pit wall as this was being explained. As we came into a relatively calm and controlled period, the safety car came out," added Dennis.
Team strategists advised to make pitstops but the instruction was not given to Montoya until after he had gone past the pitlane entrance. Raikkonen was therefore first in.
"Of course that meant that Kimi had an advantage, because he went back in the lead," said Dennis. "When Juan Pablo came in he was calm, he was not angry or frustrated.
"He was disciplined and an engineer followed the procedure which is to remind the driver to stay left of the white line (on exit) which is critical.
"What we can't do is also remind him to look for a red light.
"He rejoined the race under what he believes could even have been a blue and red light."
Dennis said that as soon as the team realised the situation, they asked race director Charlie Whiting whether Montoya should drop to the back of the grid or take a drive-through penalty. Whiting left the matter in the hands of the stewards.
"I felt the penalty was out of kilter with the crime," added Dennis.
"We made three mistakes," he said. "He made the mistake coming out after the first stop which would have given him second place in the race, we made the error on not calling him in and ultimately he made an error on going out.
"We're bitterly disappointed that we didn't have a one-two but on the other hand we can't let that disappointment detract from an excellent race win by Kimi."