The top-seeded Spaniard, playing in the tournament for the first time, beat Sluiter in 91 minutes to set up a meeting with Sweden's giant server Joachim Johansson.
"I feel good indoors," said the 20-year-old, making his first tournament appearance since his quarter-final loss to Russian Mikhail Youhzny in the U.S Open last month.
"I don't feel that rusty, I've been training really hard at home in Mallorca to prepare myself for the end of this season," added Nadal, who helped Spain beat Italy [ Images ] in the Davis Cup group playoffs two weeks ago.
Looking pumped up, Nadal broke Sluiter in the opening game of the match and never looked back.
Despite forcing the Spaniard into several tough rallies, Sluiter could not match the heavy topspin strokes of Nadal, who held his serve to clinch the first set.
He broke Sluiter twice in the second set and served it out on his first match point.
"It was a really nice atmosphere. It feels good to win some matches for the confidence," added Nadal.
Home crowd favourite Johansson, briefly ranked ninth in the world in 2005 before a shoulder injury forced him out for more than a year, outpowered Italian veteran Davide Sanguinetti to win 6-4, 6-4.
"He's one of the world's best servers, so it will be a tough match," Nadal said of the promising 24-year-old Swede, who has slipped to 690 in the rankings. "I will try my best."
The relatively slow indoor surface in Stockholm will be to the advantage of the Spanish claycourt specialist.
Belgian Kristof Vliegen, the only other seeded player in action on Tuesday, disposed of Chilean Nicolas Massu [ Images ] 6-2, 6-4.