Murray recently split from his coach Mark Petchey

The 18-year-old Briton trailed the world number 291 by a set and a break but rallied to win the second set.

With the Spaniard struggling with cramp in both legs, Murray eased through the third set to set up a clash with fifth seed David Ferrer.

Russian seeds Igor Andreev and Dmitriy Tursunov both lost on the opening day.

Andreev, seeded 11th, was beaten 4-6 7-6 7-6 by countryman Teimuraz Gabashvili while 14th seed Tursunov was beaten 4-6 6-0 6-3 by Spanish wildcard Carlos Cuadrado.

Meanwhile, 19-year-old Frenchman Gael Monfils beat Stefano Galvani of Italy 6-2 7-5.

In the next round I'm not expecting to win, but as long as I perform better, that is the main thing Andy Murray

Despite getting back to winning ways, Murray said he was "a bit disappointed overall" with his performance.

"I knew it would be a tough match as I have not played that much on clay since the French Open," said Murray, who was a losing semi-finalist at last year's junior tournament at Roland Garros.

"I didn't do anything really that well, I didn't have too many big serves and I made a lot of mistakes on my backhand.

"I kept fighting the whole match though and that was the main thing as you can always do better in the next round."

Murray began well and broke immediately, but Granollers-Pujol dominated the remainder of the set to surge into a surprise lead.

Murray will have to do better on his second serve against Ferrer From Ken Have your say on Five Live

The local player then broke to lead 3-2 in the second set, but Murray took four of the next five games to level the match.

Leading 1-0 with serve in the decider, Murray's opponent took a medical time-out, and although Granollers-Pujol returned to break serve, thereafter it was one-way traffic for the British youngster.

"I only arrived here at 10pm on Saturday night and so I've only had the chance to practise for two hours on clay," Murray added.

"I know my best surface is the hard court, although I enjoy playing on clay. I don't play enough on the surface though and this is only the third match on clay on the tour I think.