Former world number one Novak Djokovic's bid for a third Madrid Open title began with a 7-5 6-4 first-round win over Kei Nishikori.
The Japanese had reached the quarter-finals or better in each of the last five years but lost a first set littered with mistakes.
However, Nishikori kept pace with the Serbian, who has been troubled by an elbow injury, in the second set until his serve was finally broken in the 10th game and he went on to lose the match.
Tenth seed Djokovic will now play Russia's Daniil Medvedev or Great Britain's Kyle Edmund, who meet on Tuesday.
Frenchmen Richard Gasquet and Benoit Paire accounted for 14th seed Tomas Berdych and 15th seed Lucas Pouille 6-4 6-2 and 6-2 6-3 respectively.
World number 24 Milos Raonic swept past Argentinian qualifier Nicolas Kicker 6-3 6-2.
Sky Bet Price Boosts
- Rafael Nadal 2/1 to win the Madrid title without dropping a set
- Rafael Nadal 9/4 to win Madrid, Rome and French Open titles
"Nadal has continued to dominate his rivals on the clay courts in 2018, winning both ATP Monte Carlo and ATP Barcelona in some style," Sky Bet's tennis trader informed us.
"He has now racked up 12 consecutive victories this year without dropping a set, and this extends back to 24 straight set wins on the clay from last season.
"We have boosted Nadal to 2/1 from 6/4 to win in Madrid without losing a set, and we are also offering 9/4 from 7/4 that Nadal can do the winning clay court treble of Madrid, Rome and the French Open this year."