Although Sordo crashed out on day two in Portugal, the accident came when he was right on dominant points leader Sebastien Ogier's tail in the lead battle.
Citroen had been blown away by Ogier and Volkswagen in Mexico in March, but Sordo and team-mate Mikko Hirvonen made significant progress at a subsequent test.
"I said I couldn't recognise myself in Mexico, but in Portugal I recognised myself better than ever," said Sordo.
"The team did an incredible job with the car. We changed the differential, the suspension, the springs, everything and now I can go to Argentina ready to fight for the first position."
Citroen team boss Yves Matton said Sordo's pace had been so encouraging, it outweighed the disappointment of his accident.
"After he crashed, Dani came to me and he said he was sorry for what happened, but I told him: 'Dani, don't be sorry, you have shown to me what you can do - and this is the most important thing," said Matton.
"For a long time, we didn't see this kind of speed from Dani. We know he is a driver who needs to be right in his head and he is there now.
"After the crash he was not down, he was happy for himself and the team – it is very important."
Ogier's victory and team-mate Jari-Matti Latvala's podium in Mexico meant that VW moved past Citroen and into the lead of the manufacturers' title race for the first time this year.
But Citroen's star driver Sebastien Loeb returns for Argentina, where he has not been beaten since 2004.
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