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 Britain's Kyle Edmund, who meet today.
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.
Also in Madrid, former world number one Maria Sharapova recorded back-to-back wins for the first time since January to book her place in the last 16 of the Mutua Madrid Open.
The Russian cruised to a 7-5 6-1 victory over Irina-Camelia Begu and afterwards spoke of the readjustments she has had to make following injury and a change of coach.
"It just took time for me re-evaluate where I was, where my body was," Sharapova, who returned to former coach Thomas Hogstedt after splitting with Sven Groeneveld, told her post-match press conference.
"I also made changes within my team; especially in that period of time, it was not easy.
"There's never a bad time to make a good change. You do hope that those changes lead to better things and good things.
"It's not because the past necessarily wasn't working, but because you believe that there could be better things to come."
Sharapova now faces Kristina Mladenovic, who was runner-up in Madrid last year and victorious over the Russian in the semi-final of the 2017 Porsche Tennis Grand Prix in Sharapova's first tournament following a 15-month ban due to an anti-doping rule violation.
Second seed Caroline Wozniacki staged a thrilling late comeback to beat Ashleigh Barty 6-2 4-6 6-4.
The Australian Open champion found herself staring at defeat at 4-2 in the final set but won four in a row to prevail in two hours and five minutes and will face former French Open semi-finalist Kiki Bertens, who beat Anastasija Sevastova 6-1 6-4.
Mladenovic was taken to three sets by Shuai Zhang, eventually winning 6-4 4-6 6-3.