Alonso, who roared to an unlikely victory on the same circuit in a far less competitive car a year ago, started third on the grid and damaged his front wing when he nudged pole-sitter Sebastian Vettel on turn two while fighting for the lead.
"Today, unfortunately, we were very unlucky. After making a good start, I touched with Vettel at the second corner: it was a surprise to find him there, almost stopped and I don't know what speed he was doing," Alonso said in a team release.
With all drivers starting on intermediate tyres following a heavy downpour, Alonso struggled for grip due to his damaged wing and was challenged for second place by Vettel's Red Bull team mate Mark Webber towards the end of the opening lap.
The Spaniard opted against coming into the pits to repair the damage and his race was soon over as the front wing gave way and became wedged underneath his car as Webber overtook him on the finishing straight.
"Despite the fact the car was damaged, it didn't seem to be too bad and, together with the team, we decided to keep going," said Alonso.
"If we'd stopped immediately and then again on lap three or four to fit dry tyres, we would have dropped too far back and definitely lost the chance to finish up the front."
The stricken Ferrari slid into the turn one run off area and the double world champion was soon making the long and lonely walk back to the paddock, fuming inside his helmet.
"It's easy to criticise this decision, but at the time it seemed like the right one," the Spaniard added.
"It was certainly a shame, because here we could have fought with the Red Bulls, but circumstances didn't help and apart from the wisdom of the decisions we took, bad luck really played its part."
The race was won by Vettel, who led a Red Bull one-two ahead of Webber with the Mercedes duo of Lewis Hamilton and Nico Rosberg filling the next two places, ahead of Felipe Massa in the other Ferrari.
Ferrari lost their lead in the constructors' championship to Red Bull while Alonso, last year's overall runner-up, slipped from second to sixth.
"As soon as Fernando collided with Vettel, it was clear that his race would involve fighting his way up the order," team principal Stefano Domenicali said.
"At that time, we felt the front wing could hold out and on a track that was progressively drying out, we risked leaving him out. With hindsight, it did not work out, trying to avoid doing two stops in the space of just four laps."
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