American fifth seed Sam Querrey secured a place in round two of the Ricoh Open at s'Hertogenbosch when he battled past Benjamin Becker of Germany 7-6 (7/3) 7-6 (7/5).
There was also progress for eighth-seeded Frenchman Nicolas Mahut on the opening day of the grass-court season as he beat Lukas Lacko of Slovakia 6-1 6-4.
The wild card will next meet compatriot Paul-Henri Mathieu after his 6-4 6-4 victory over American Rajeev Ram.
Highlights: Djokovic beats Sonego to set up Nadal final
British number two Aljaz Bedene set up a clash with second seed Bernard Tomic following a 7-6 (7/5) 6-2 first-round win over qualifier Ernesto Escobedo of the United States.
Yoshihito Nishioka of Japan is out, though, after he went down 6-1 2-6 6-3 against American Stefan Kozlov.
At the Mercedes Cup in Stuttgart, both Samuel Groth and Michael Berrer progressed to the second round.
Australian Groth beat Illya Marchenko of Ukraine 7-5 6-4, while German Berrer came through in three sets against Tunisia's Malek Jaziri, winning 6-7 (7/9) 6-2 6-4.
In qualifying, Czech Radek Stepanek defeated Great Britain's James Ward 6-2 6-1.
Nadal beats Opelka in Rome semi-final
Djokovic to face Nadal in the final at the Italian Open for sixth time