Brazilian Felipe Massa took a five-place grid penalty for the US Formula One Grand Prix to help Ferrari team mate Fernando Alonso on Sunday.
Massa qualified ahead of the Spaniard, who is the only driver who can deny Red Bull's Sebastian Vettel a third successive title. Vettel, with a 10-point lead and one race remaining after Austin, starts on pole position.
Ferrari said they had broken a seal on Massa's gearbox, incurring the mandatory penalty, for "strategy considerations, with the objective of maximizing Alonso's start potential."
The penalty means Alonso will now start in seventh place and, crucially, on the 'clean' side of the grid.
"We saw yesterday that starting from the dirty side of the track would have been penalising: there was a significant risk of finding ourselves too far behind the leaders at the end of the first lap," Ferrari said on their website.
The team said both drivers had agreed the move.
"We've always maintained that the interests of the team come before that of the individual drivers and this has always been our very transparent policy," said Ferrari.
"Felipe has fully comprehended the reasons behind this decision and so he's once again proven his total dedication to the team - something for which we would publicly like to express our gratitude."