The 22-year-old Spaniard won for the 52nd time this season by seizing control after struggling to capture the first set against his 27th-seeded German foe.
"I was a little bit nervous because for me it was important to finish the match," Nadal said. "And, well, lucky for me later I played a good game (to win the match)."
Also Saturday, eighth-seeded Richard Gasquet topped Gilles Simon 6-3, 6-3, 3-6 (3-7), 6-3; No. 17 Mikhail Youzhny of Russia topped No. 16 Radek Stepanek of the Czech Republic 5-7, 7-6 (7-5), 4-6, 7-6 (7-4), 6-3; and unseeded Marin Cilic of Croatia knocked off No. 14 seed Paul-Henri Mathieu 6-7 (5-7), 6-3, 6-4, 7-6 (8-6).
Other winners were 12th-seeded Andy Murray, Rainer Schuettler, Arnaud Clement and the 25th seed, Dmitry Tursunov of Russia.
Penelope Cruz named 2013's 'Best Body' by Fitness magazine
Video of Victoria’s Secret models trying to 'twerk' hits Instagram