World number one Murray overcame Feliciano Lopez in two hard-fought sets, while Nadal's 50th win in Barcelona came in straight sets against Kevin Anderson and Thiem beat his second Brit of the week in Dan Evans.

An early exit in Monte Carlo and Bernard Tomic's withdrawal in the previous round left Murray short of match practice on clay, and errors crept into the Scot's game.

The mercurial Lopez combined brilliance on both flanks with just as many mistakes, however, with Murray wrapping up each set on the back of his opponent faltering.

Albert Ramos-Vinolas eliminated Murray at the Monte-Carlo Masters and the Scot will have a swift chance at revenge, with the pair going head to head in the last eight.

Nadal won his 10th Monte Carlo title last week and could match the feat in Barcelona, having had the centre court at the Real Club de Tenis named after him.

Anderson rarely looked like putting up much resistance, winning only nine points off the Nadal serve as the home favourite booked a quarter-final against Hyeon Chung - one of several surprise winners in Thursday's other matches.

Chung beat Alexander Zverev (8) 6-1 6-4 in a fine display, while Karen Khachanov beat fifth seed David Goffin and Benoit Paire (17) was eliminated by Horacio Zeballos.

Lucky loser Yuichi Sugita continued his fine run with a 6-3 6-3 win over seventh seed Pablo Carreno Busta to set up a meeting with Thiem (4) in the next round.

Already with one clay title under his belt this year in Rio de Janeiro, Thiem has looked in fine form so far this week and took his record on dirt for 2017 to 9-1 with a composed win over Evans.