Andy Murray admitted he missed a gilt-edged chance to reach his second Masters series clay court semi-final in Madrid.

The British number one and world number three had a chance to serve for the first set against Argentina's Juan Del Potro, a player he had beaten in two of their previous three encounters.

But he slipped up when it mattered and then saw the world number five take control, closing out the match 7-6, 6-3.

However, he tried to stay upbeat ahead of the second Grand Slam of the season in Paris, now just one week away.

"I had my chances but it wasn't my best game," admitted Murray.

"It didn't help that I bust a string when 5-2 up in the first set and I lost eight points in a row after that.

"The returns were a problem and that is something I will need to work on before the French Open.

"He's a very good player, the number five in the world but I don't feel like at any point I was outclassed.

"My confidence on clay is still improving."