UPDATE 1-Tennis-Open-Murray capitalises on Cilic's mistakes

* Murray reaches French Open quarters for first time

* Cilic says thigh injury was bothering him

(adds quotes, details, byline)

By Sonia Oxley

PARIS, May 31 (Reuters) - Third seed Andy Murray made the most of Marin Cilic's errors to reach his first French Open quarter-final on Sunday, clobbering the Croat 7-5 7-6 6-1.

The 22-year-old Murray, seeking his maiden grand slam title, became only the third British man to reach the Roland Garros last eight since tennis turned professional in 1968.

It was the first time the Scot had won four matches in a row on clay and with the early exits of favourites Rafael Nadal and Novak Djokovic, he has hit good form just when the championship has been thrown wide open.

"I'm playing well. I mean, you don't get to the quarters of the French not playing good claycourt tennis," said Murray, who had enjoyed an excellent clay season by reaching the Monte Carlo semi-finals and Rome quarter-finals before arriving in Paris.

"This claycourt season has been good. It's been much better than in previous years. I try and keep improving."