(Reuters) - Costa Rica coach Jorge Luis Pinto urged referee Ravshan Irmatov to keep a close eye on Dutchman Arjen Robben in Saturday's World Cup quarter-final against the Netherlands.

"We are really worried about Robben's diving," Pinto told reporters on Friday.

"I would like to ask FIFA and the referees to watch out and be very careful because this is very important and this could have a huge impact on the result."

Robben, who has been one of the tournament's standout players with a string of impressive displays and three goals in Brazil, caused a storm when he admitted that he had dived in the first half of Sunday's last-16 2-1 win over Mexico.

The rapid forward went on to win a stoppage-time penalty after going down easily under a challenge from Rafael Marquez which striker Klaas-Jan Huntelaar converted to seal victory.

"I think Robben is one of the three or four best players in the world," Pinto said.

"But on the other hand we have to say that there have been refereeing mistakes and referees have to watch out - we are really worried about Robben's diving.

"He admitted he dived, so I hope that the referee and the assistant referees are very careful tomorrow. I respect FIFA and the referees very much but I tell them, please watch out."

Pinto was speaking on the eve of Costa Rica's first ever quarter-final appearance after a dream run in Brazil that took them through a tough group thanks to a solid defense and some gutsy counter-attacking displays.

On Saturday they face a Dutch side who destroyed defending champions Spain 5-1 in their opening group game on their last visit to Salvador's Fonte Nova arena.

"(The Spain match) sends no shiver down my spine at all," Pinto said. "Of course I respect them, but we have played against England, Italy, and even Greece is a very difficult team. We are never scared, we respect them but we will try to control them."

Pinto will have goalkeeper Keylor Navas fit for the clash after he recovered from a shoulder injury. The stopper has been in fine form for the Costa Ricans and was the hero of their shootout triumph over Greece in the last round.

"He has played very well in Europe and Spain and in our national team and of course that makes us very confident and it makes us very difficult to play against," Pinto said.