Ruthless Rafael Nadal maintained his ominous form on clay by beating Andrey Kuznetsov in straight sets to reach the third round of the Madrid Open.

Nadal has claimed back-to-back tournament victories in Monte Carlo and Barcelona and the 14-time grand-slam champion started his quest to win a fifth Madrid Open title by seeing off unseeded Russian Kuznetsov 6-3, 6-3.

Defending champion Andy Murray began his defence of the title with a 7-6 (7/3), 3-6, 6-1 win over 37-year-old Czech Radek Stepanek to remain on course for a semi-final meeting with Nadal.

The world number five Nadal produced a commanding service display and wound up his forehand with great effect, putting on a show for a partisan crowd to set up a third-round meeting with either Sam Querrey or Lucas Pouille.

Nadal won 80 per cent of points on his first serve and did not face a solitary break point, with one break in the first set and two in the second seeing him through as he eyes a 50th title on the red surface.

The fifth seed, beaten by Andy Murray in the final of this event last year, had won 10 matches in a row before taking to the court on Tuesday and made his presence felt by holding to love and breaking in the second game when Kuznetsov was long with a forehand.

Nadal did not allow Kuznetsov a way back in the first set and won four games in a row in the second to ease into round three and make it three wins out of three against the Barcelona Open quarter-finalist.

Murray needed three sets to overcome Stepanek, but eventually got the job done in just under two-and-a-half hours on court.

Eleventh seed Milos Raonic also booked his place in the last 16 with a 6-4, 6-7 (3/7), 6-2 win over Ukrainian Alexandr Dolgopolov.

World number one Novak Djokovic begins his campaign after a three-year absence in Madrid on Wednesday against Borna Coric.

Frenchman Gael Monfils continued his fine form after losing to Nadal in the final of Monte Carlo last month as he saw off Kevin Anderson 6-4, 6-1.

Controversial Australian Nick Kyrgios set up an enticing second-round clash with fourth seed Stanislas Wawrinka as he battled past Argentine Guido Pella 7-6 (9/7), 6-4.

A dreadful week for Bulgaria's Grigor Dimitrov continued as he exited in the first round 7-6 (7/3), 6-3 to Pablo Carreno Busta two days after defaulting in the final of the Istanbul Open for a racquet-smashing tirade.

And former US Open champion Juan Martin del Potro scored an impressive 7-6 (7/5), 6-3 win over in-form 14th seed Dominic Thiem.

In the women's Madrid Open there was a better day for the favourites after a series of high-profile exits left just five seeds left in the draw.

World number seven Simona Halep thrashed Karin Knapp 6-1, 6-1 to set up a third-round clash with Timea Bacsinszky as the 10th seed overcame Ekaterina Makarova 6-4. 5-7, 6-4.

Spain's Carla Suarez Navarro booked her place in the last 16 with a 6-3, 6-2 win over Germany's Sabine Lisicki.

Sam Stosur and Anastasia Pavlyuchenkova also reached the third round without having to hit a ball as 11th seed Lucie Safarova and Camila Giorgi withdrew