Murray won 61 percent of the points in the match in cruising to a 6-1, 6-2 victory over Santiago Giraldo. Murray had nine aces and lost his serve just once on the day.
Top-seeded Rafael Nadal, who has won the event six times in the last seven years, lost just 12 points in eight games serving during a 6-2, 6-3 win over Robert Farah. Nadal, in addition to winning 71 percent of the points on serve, took 55 percent off Farah's serve.
No. 3-seeded David Ferrer, who has been the runner-up the last three times Nadal won the tournament, advanced to the quarterfinals with a 6-0, 6-2 victory over Albert Montanes. He saved all four of the break points he faced.
Other match results Thursday saw fifth-seeded Janko Tipsarevic stop Frederico Gil 6-2, 6-2; No. 7-seeded Feliciano Lopez rip past Jarkko Nieminen 6-3, 6-1; eighth-seeded Kei Nishikori top No. 17 Albert Ramos 7-6 (7-2), 6-3; No. 9-seeded Fernando Verdasco cap the day's play with a 6-4, 6-4 decision over No. 13 Kevin Anderson; and 11th-seeded Milos Raonic pull a mild upset by beating sixth-seeded Nicolas Almagro 6-3, 6-3.
Nadal goes against Tipsarevic and Verdasco plays Nishikori in Friday quarterfinals in the same half of the draw. The other matches have Murray facing Raonic and Ferrer taking on Lopez.
Swim Week Miami Beach 2014 [PHOTOS]