Rafael Nadal has secured his passage into the fifth round of the Miami Masters after overcoming Japanese number one Kei Nishikori 6-4 6-4.

The Spaniard was surprisingly broken by his opponent early in the opening set, but he quickly broke back before securing a break of his own to take the first set 6-4.

Nadal continued his dominance early in the second set, holding serve before breaking Nishikori to move into an early 3-0 lead.

The world number two looked on course for a comfortable victory when he moved 5-2 ahead, but the 22-year-old secured two straight games to pull to within one game of Nadal.

Nadal secured the win with a break, however, as Nishikori sliced wide.