“When you work for the Ferrari team you know the team was the centre of the decision. I have to thank Felipe for that”
Massa would have started sixth, two places ahead of Alonso, but Ferrari broke the seal on the Brazilian's gearbox, a move that carries a mandatory five-place grid penalty.
The decision was made because the new Circuit of the Americas track area off the racing line - the even-numbered side of the grid - was very short of grip. Engineers were predicting that drivers on that side of the grid would lose two places at the start.
Faced with needing Alonso to finish at least fourth if his title rival Sebastian Vettel of Red Bull, who was on pole, won the race, Domenicali felt he needed to do everything he could to help Alonso's chances of a strong result.
The Spaniard made a superb start from seventh to run fourth on the first lap.
He finished third
following the retirement of Vettel's team-mate Mark Webber with alternator failure.
Vettel was beaten into second place by McLaren's Lewis Hamilton and goes to the final race of the season in Brazil next weekend with a 13-point advantage over Alonso.
Domenicali said: "It is something that is within our possibility to do it.
"We knew before the race that the difference between the two sides of the grid was very high and we knew that if we were thinking of trying to achieve Brazil as the last race it would have been very important to be the front car for the first couple of laps otherwise the race would have been more difficult.
"When you work for the Ferrari team you know the team was the centre of the decision. I have to thank Felipe for that. He drove extremely well all weekend and this is something that is positive for Brazil because we need both our drivers doing a great race if we want to challenge Vettel to win the drivers' title.
"Now we need to make sure they will be tense up to the last minutes up to the chequered flag."
Alonso said: "We were maybe thinking to arrive in the first corner ninth and 10th or something like that so changing the grid positions we were hoping for better result and we were lucky and it was the truth.
US Grand Prix - top three drivers
"[I'm] proud of this decision but more proud of this decision to say the truth, sometimes when teams take decisions not many people say the truth."
Red Bull team boss Christian Horner said he understood Ferrari's decision.
"It's within the regulations; it's a tactical move," he said.
"They obviously made that decision to get Fernando on to the right hand side of the grid and it worked well for him.
"It's within the rules, obviously hard on Felipe but their priority is Fernando."
Massa, who climbed up from 11th on the grid to finish fourth behind Alonso, said: "It was very hard definitely, to give five places like that to help your team-mate and your team is not easy.
"But I did it for the best of the team and Fernando because he needs all the help to win the championship.
"I did the maximum I could but I was not happy - it is impossible to be happy, [but] I think I did the right thing. The race I did was really fantastic. It was definitely the best of the year and like a victory for me."
McLaren team boss Martin Whitmarsh said he felt it was a "tough" decision, particularly on those other drivers who were moved to the dirty side of the grid as a result, which was Force India's Nico Hulkenberg, Lotus's Romain Grosjean and Williams's Bruno Senna.
Whitmarsh said: "Team principals can decide how they run their programmes. It's very clear [Ferrari] are very focused on Fernando and, in fairness, it works for Fernando.
"It was not doing those things that meant Fernando left us [at the end of 2007] and he's a great racing driver.
"They've got to make their decisions - I'm not criticising anyone for what they do. We've got to go racing as we see as a good way to go racing.
"I think the toughest thing was that it put a number of people on to the slow side of the grid.
"Sadly it didn't impact on us at all - we were on the slow side of the grid and stayed on it - but if I had earned a place on the fast side of the grid and that had put me on to the slow side I would have been pretty exercised about it."
United States Grand Prix 2012, day three
Sunday, 18 November: Highlights repeat; 0200-0400, BBC Two
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