Murray extended his perfect record against Lopez to 9-0 with a 6-4 6-1 victory in 73 minutes to set up a clash with France's Jo-Wilfried Tsonga, who recovered from 5-1 down in a second set tie-break to beat Marcos Baghdatis in three sets.
World number six Murray made the ideal start with a break of serve to love in the opening game of the match, but there was a moment of concern in the next game when he grabbed his lower back in pain after dumping a forehand into the net.
The Scot went on to lose that game after saving two break points, but did not appear to be physically hampered afterwards and he soon broke Lopez again for a 3-2 lead.
Murray lost just one point in each of his next three service games to serve out the set and again broke Lopez at the start of the second set.
Lopez looked to be suffering from back problems of his own and never threatened to get back into the contest, losing his serve twice more as Murray sealed victory with a casual backhand return winner down the line.