Raimund claimed the title with a final jump of 106.5 metres and 274.1 points, 3.4 points ahead of Tomasiak, while bronze medallists Nikaido and Deschwanden finished 8.1 points back.
The 25-year-old Raimund fired an early warning on a dark but clear night in the Italian Alps, soaring 102 metres in the first round to earn the final jump of the competition and then handled the pressure to fly to his first Olympic gold.
“I know there’s a lot of pressure from the media and outside but my coach, the whole staff, my girlfriend... they were taking all that off my shoulders so I could just concentrate on myself. I want to say thank you to everybody," he said.
“I'm extremely proud of myself that I could do two amazing jumps and stand on top at the end.”
The 19-year-old Tomasiak was delighted with second place.
"It is a dream coming true. I wasn’t really expecting that at my first Olympics. I’m a little surprised, but very happy. I jumped really good," he said.
Gold-medal favourite Prevc of Slovenia got off to a rocky start, finishing eighth in the first round, with the World Cup leader looking disappointed as he realised he had landed too short to mount an early challenge for gold.
His 105-metre second-round jump bumped him briefly into first place but he ended up out of the medals.
"Already the small (normal) hill is difficult for me and there was a bit of back wind but, honestly, after yesterday's training I did not expect too much," he told Reuters.
Prevc added that he had approached the competition with the mindset that he would be satisfied with a top 10 finish.
"It's on one hand success for me, but on the other hand I of course came here to win medals and, yeah, it's a little bit (of a) salty feeling."