Murray extended his perfect record against Lopez to 9-0 with a 6-4, 6-1 victory in 73 minutes to set up a meeting 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 No.6 Murray made the ideal start with a break of serve to love in the opening game, but there was a moment of concern in the next 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. The Spaniard looked to be suffering from back problems of his own and never threatened to turn around the contest, losing his serve twice more as Murray sealed the win with a backhand return winner down the line.
"I moved well, returned well," Murray said. "It's not always that easy to feel comfortable against him because there is not [a lot] of rhythm with the way he plays."
Murray struck nine winners in the 44-minute opening set, in which Lopez committed 17 unforced errors. He broke Lopez's serve thrice in the second set, winning 24 of 36 points.
"I'm just looking forward," Murray added when asked about his goals. "It's nice that winning Wimbledon has been sort of accomplished, but I look forward now to try and do more in the big events."
Meanwhile, Colin Fleming and Jamie Murray both faced new opponents in the first round in Miami of the men's doubles but both bowed out in straight sets.
Fleming and Ross Hutchins were due to play a local wildcard duo but then drew the shortest of short straws after being paired instead with the world's top team, US twins Bob and Mike Bryan. The Britons ran the top seeds close before going down 6-4, 6-4. Murray and John Peers lost 6-4, 7-5 to the No.6 seeds, Daniel Nestor and Nenad Zimonjic.