The Spaniard continued his comeback from a knee injury that had kept him out of action for three months with a straightforward victory versus the German qualifier to move into the quarter-finals of an event he won in 2005.
Martin Klizan will be the Spaniard's opponent in the last eight after he benefited from a retirement by Latvia's Ernests Gulbis, who was trailing the Slovak 6-2 3-0 when he withdrew due to a right shoulder injury.
And Nadal believes he has much to work on ahead of his encounter with Klizan.
"In general I need to improve. It's obvious," Nadal said. "My serve worked well today. But in general I need more rhythm on the legs, more rhythm on the shots.
"I am playing okay, trying to not miss a lot, trying to play with not too many risks. That's what I did today. It's the only way to have matches, only way to have rhythm."
With the exception of Gulbis, all of the seeds in action at the ATP 500 hard-court tournament on Thursday enjoyed serene progress, with sixth seed and two-time grand slam champion Andy Murray continuing his recent return to form.
Brit Murray won 73 per cent of points on his first serve and broke Pablo Cuevas five times on his way to an easy 6-2 6-2 triumph against his Uruguayan counterpart.
Murray will now face US Open champion Marin Cilic following his 6-3 6-3 success over Joao Sousa of Portugal in which the Croat lost just 10 points on serve.
Elsewhere in the draw, Grigor Dimitrov beat Pablo Andujar 6-4 6-4 to set up a repeat of this year's Wimbledon semi-final with world number one Novak Djokovic, while Tomas Berdych overcame Victor Troicki 6-3 6-4.