Fernando Torres missed three chances, including one from close range in the last five minutes, while Gary Cahill was also denied when well placed.
"They had one clear chance and they scored and we didn't take our chances. That was the difference," said Benitez.
"We had four very good opportunities. Their goalkeeper was man of the match."
Benitez, who became the first boss to lead a side in three Club World Cup finals after winning with Inter Milan in 2010 and losing as Liverpool manager in the 2005 final, added: "We knew it would be a tough game against a good team.
"They were very physical from the first minute, in every challenge, every ball.
"Every second they were around the referee, doing well, and wasting time at the end."
Frank Lampard, the Chelsea captain for the game as he returned to the starting line-up for the first time in almost two months after a calf injury, believes his side must quickly focus on domestic football.
Thirteen points behind Premier League leaders Manchester United, they now face a hectic period of six games in 18 days, beginning with a League Cup quarter-final against Leeds United on Wednesday.
He said: "We now have to go on a run of games in the league to keep ourselves in the hunt and we have the FA Cup and League Cup as well so we have to keep pushing on.
"We knew what Corinthians would bring but it's just disappointing to get all the way out here and not win.
"It was always going to be a tough game and they're a good team. But we're coming away with that bad feeling that we had enough chances to at least draw the game."