Nascimento was floored by a heavy right hook in the first round but battled on admirably and rocked Parker with a couple of heavy shots in the sixth as he opened up a cut near Parker's left eye.
Parker was also bleeding from his ear in the sixth and it was a testament to his ability to take a punch that he bounced back in such strong fashion in the seventh.
"In boxing these things happen and sometimes you get caught with a good one," Parker said. "But I took it and it wasn't as bad as I thought it was and I was just moving around to try and get away from him loading up."
Trainer Kevin Barry was pleased with his young charge who continued his boxing education in solid fashion.
"Was he as sharp as he's ever been? No, he wasn't. He was a little bit flat tonight," Barry said.
"In the dressing room he was like lightning. I thought, by God we're going to be in for an impressive performance tonight.
"I don't know what it was but when the fight started he was a little flat. Joe said to me, the rhythm wasn't quite there. Sometimes you are like that. If you can have a flat night at the office and still come away with a belt and a knockout victory, it's not a bad night."
Parker's victory saw him claim the WBA PABA interim heavyweight title and will have given him valuable ranking points within the organisation.
Fighting on an undercard of a world heavyweight title fight was a steep learning curve for Parker, 22, and his handlers were keen to show him off to the global TV audience.
Despite Parker's jitters, a sold-out Konig Pilsener Arena were treated to another sharp performance, while Nascimento, who came in to the bout with a 17-5 record, proved a durable opponent.
Parker, who fought in gold trunks with purple trim, looked quick in the ring, although wasn't as active as he may have liked.
"I felt a bit off. Maybe I was a little tired but these things happen in boxing. Just fortunate to come away with a win," Parker said.
"The most important thing was I was able to work the punches and come out with the victory in the end.
"Parker's early plan to attack the body worked in his favour and he won every round of the bout except the sixth.
After flooring him in the first, Parker relied a bit too much on his right hand but eventually produced a heavy burst in the seventh, which brought him the win.
- Daniel Richardson travelled to Germany courtesy of Duco Events Ltd
