Lionel Messi acknowledged that his failure to convert a penalty had been costly as Argentina succumbed to a 2-0 friendly defeat to Brazil in Beijing.
Argentina fell behind when Atletico Mineiro striker Diego Tardelli punished a defensive lapse by Federico Fernandez and Pablo Zabaleta in the 28th minute, but Gerardo Martino's men could have drawn level before the break after Danilo was adjudged to have brought down Angel Di Maria in the area.
However, Jefferson saved Messi's spot kick, and Brazil were able to add to their lead in the second half through Tardelli's header.
"We were always trying to win the match but we couldn't," Messi said in quotes published on Argentina's official Twitter feed. "The match was determined by our two errors.
"The error in the first goal and the penalty were the defining factors. If it had been converted, it would have changed the match.
"We were better at the start but didn't take advantage. They scored with the first clear chance they had."
He added: "The team is going through a process of change with a new coach, and it takes time. With training and matches we will adapt to what Martino wants, and we will succeed."
Martino, who replaced Alejandro Sabella after the World Cup, said the opening goal had come against the run of play.
"We made mistakes that, against national teams like Brazil, prove costly," the former Barcelona boss said. "Equally, I take away positive things."
#INSERT type:image caption:Jefferson did his homework to stop Lionel Messi from the penalty spot. END#
Meanwhile, Jefferson revealed that he and Brazil goalkeeping coach Taffarel had studied Messi's penalties.
The 31-year-old Botafogo goalkeeper told Globo that he had left it as long as possible before moving in order to make life tough for the Argentina captain, whose failure to score from the spot was the 13th of his career.
"I have studied the way Lionel Messi takes penalties," he said in quotes translated by Goal.com. "I waited until the very last second to dive, so the penalty-taker has less chance. He took it on his best side, and I was very happy to save it."
Brazil goalkeeping coach Claudio Taffarel also said Jefferson's late dive had been key to stopping the spot kick, explaining: "We always study penalties before a game, but Messi is someone who shoots with ease both on the left and the right.
"Jefferson's greatest secret is that he stands still until the last minute. He made a great save. I joked with him at half-time, saying his save was worth double... after all, we're talking a penalty save against Argentina, and against Messi."