"I was so confident I could score it but that's football," said Joaquin. "It was my turn to take one but I missed it.
"We really believed we were going through.
"In extra time I had a little thigh strain but I was fine to take the penalty."
Joaquin provided the cross from which Fernando Morientes thought he had scored the golden goal in extra time.
But the effort was ruled out after the linesman flagged for the ball being out of play when Joaquin played the cross into the Korean area.
Television replays showed it was a wrong decision.
"The ball didn't even touch the line, let alone go over it," Joaquin said. "It was a big surprise when the flag went up.
"That's football. If that goal had been given we'd be looking at the semi-final now."
The penalty miss by Joaquin was also harsh on the player as he had arguably been Spain's best player throughout the match.
"I tried to give everything in that game but in the end I missed my penalty and we've gone out.
"I'm a bit down," he concluded.