Christian Wück's Germany bossed the opening period and went close through Klara Bühl, Jule Brand and Nicole Anyomi as goalkeeper Cata Coll was forced into making several smart stops.
The Spanish team improved in the second half and Esther González hit the woodwork. However, stars Alexia Putellas and Aitana Bonmatí failed to shine.
Over 40,000 fans roared Germany on and Bühl continued to be a threat, striking a post herself. Shekiera Martinez also spurned a glorious opportunity for the Germans late on.
"I'm annoyed because we haven't been rewarded," Wück told ZDF. "But we are looking forward to the next leg and know that we can not only go toe-to-toe with Spain, but also impose our game."
But the visitors will be the happier ahead of the second leg of the final on Tuesday at the Metropolitano in Madrid.
"It's a positive result and we'll see them at the Metropolitano," Coll said. "We knew they were going to come at us and have their chances. The Spanish fans never disappoint and I hope they cheer us on as always."
World Cup champions Spain, who lost this year's Euros final to England, are gunning to retain the Nations League title they won last year.
The German women have not won a big tournament since taking gold at the 2016 Olympics and are seeking revenge following their Euro semi defeat to the Spaniards.
"I am very proud of the team, we were very brave and very aggressive in the tackle and that gave Spain a real challenge," Bühl said as she looked ahead to the second leg.
"It is nice to see that we are creating chances."
Hosts France beat Sweden 2-1 in the first-leg of the playoff for third place.
Sakina Karchaoui opened the scoring from the spot in first-half added time before Stina Blackstenius equalised in the 67th minute.
Griedge Mbock Bathy sent the locals home happy when she netted the winner in the sixth minute of added time to deflate the Swedes ahead of their return leg.
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