Rafael Nadal has got the defence of his Madrid Open title off to a winning start with a straight-sets victory over Steve Johnson.

The Spaniard was made to work hard during the match before eventually coming through 6-4 6-3 in 75 minutes.

There was little to separate the pair at the start of the opening set, but Nadal eventually forced a break of serve on his way to closing it out 6-4.

It was a similar story in the second as American world number 54 Johnson dug in his heels against the four-time champion.

However, Nadal broke to take a 4-3 lead before seeing off Johnson to set up a last-16 clash with Italy's Simone Bolelli.