KEY BISCAYNE, FLA. - Two-time champion Novak Djokovic and three-time runner-up Rafael Nadal were a pair of fourth-round winners at the $3.973 million Sony Ericsson Open, a hardcourt ATP Masters tournament.

The world No. 1 Djokovic improved to 17-2 this year by dismissing 17th-seeded Frenchman Richard Gasquet 7-5, 6-3 at Crandon Park.

The reigning Australian Open, U.S. Open and Wimbledon champion Djokovic beat Nadal in last year's final, also titled here in 2007, and was the Miami runner-up in 2009.

Up next for Djokovic will be fifth-seeded Spaniard David Ferrer or 11th-seeded Argentine and former U.S. Open champ Juan Martin del Potro.

The second-seeded former world No. 1 Nadal handled 16th-seeded rising Japanese Kei Nishikori 6-4, 6-4 in 2 hours, 10 minutes. The Spanish great moved on with the help of four service breaks, compared to only two for a game Nishikori.

In addition to losing to Djokovic here last year, Nadal also finished as the Miami runner-up in 2005 and 2008.

The 10-time major champion Nadal, who owns a co-record 19 Masters titles, will face sixth-seeded Frenchman Jo-Wilfried Tsonga or 19th-seeded German Florian Mayer in the quarterfinals.

Nadal is seeking his first title anywhere since capturing the French Open last June.

Fourth-seeded Andy Murray eased into the quarters with a 6-3, 6-4 victory over 13th-seeded Frenchman Gilles Simon. The three-time Grand Slam runner-up from Scotland broke Simon twice while holding his serve throughout on Tuesday.

The 2009 Miami champion Murray will meet tough Serb Janko Tipsarevic in his next outing.

Eighth-seeded American Mardy Fish snuck into the quarters with a 6-3, 6-7 (2-7), 6-3 victory over 12th-seeded Spanish clay-court stalwart Nicolas Almagro in 2 hours, 35 minutes, while a ninth-seeded Tipsarevic reached the round of eight by getting past talented 20-year-old Bulgarian Grigor Dimitrov 7-6 (7-3), 6-2 on Day 7.

The 2012 Miami champion will collect $659,775.