By Iain Rogers

GNIEWINO, Poland (Reuters) - Spain's nervy 1-0 win over Croatia that put them into the last eight of Euro 2012 as Group C winners showed they have learned how to get through tough matches when playing poorly, according to Andres Iniesta.

However, the world and European champions are not unbeatable and extending their run of title wins is getting harder all the time, the midfielder told the daily El Pais as Spain prepare to battle France for a semi-final place later on Saturday.

"In the past we suffered and we were out," said the 28-year-old, Spain's stand-out player at the tournament being co-hosted by Poland and Ukraine.

"Now we suffer, we win and we are through to the quarter-finals," he added, with Spain having been unbeaten in their last 17 competitive matches with 16 wins and a draw.

"We have made the exceptional into something routine, which means winning is the norm, and it seems like we are invincible," said Iniesta. "But we are not and sometimes you lose even when you are the superior team."

Spain have never beaten France in six competitive meetings, losing five and drawing one, and were eliminated by Les Bleus 3-1 in a last-16 clash at the 2006 World Cup, a game Iniesta said had left him with bitter memories.

However, he said he hoped Spain would maintain their incredible streak at major tournaments and get used to winning in the same way his club Barcelona have managed in La Liga and the Champions League.

"Each year it becomes harder because winning is more difficult for us each time," he said.

"I experienced that at Barcelona and now I am experiencing it with the national team.

"It's just as hard to win the first time, when you are not in the habit, as it is to keep winning when you have achieved everything.

"That was the merit of Barcelona and I hope it will be the merit of the national team too."

The winners of Saturday's quarter-final will meet Cristiano Ronaldo's Portugal in the last four.

(Editing by Ken Ferris)