Nadal has not played since pulling out of his semifinal against Federer at Indian Wells last month because of an injury to his right knee. Nadal said Monday he resumed practice two weeks ago and feels fit.
Top-ranked Novak Djokovic faces unseeded Philipp Kohlschreiber in the second round on Tuesday. Djokovic has won eight of their 10 matches, but Kohlschreiber recently beat him at Indian Wells.
Also on Monday, 10th-seeded Daniil Medvedev; No. 11 Marco Cecchinato; No. 13 Fabio Fognini, and No. 16 David Goffin advanced, but No. 12 Nikoloz Basilashvili and No. 17 Kyle Edmund went out.
Medvedev did not face a break point in a 6-1, 6-1 win against Joao Sousa. Cecchinato, a French Open semifinalist last year, was leading 4-0 when Damir Dzumhur pulled out with an abdominal injury.
Goffin won 6-1, 6-4 against qualifier Guido Andreozzi, but Fognini had a tougher match.
The hot-tempered Italian player had the crowd on his side as he rallied to a 4-6, 7-5, 6-4 win against unseeded Russian Andrey Rublev.