The Dutchman recovered from 4-2 down to take six of the following seven legs to claim his fourth Players Championship title of the year, securing the £15,000 top prize.
"It was kind of a nervy final. I went behind after missing some doubles," said Nijman.
"I’m so happy I kept it together. There were some finishes I hit with the last dart, the 57 (to go 6-5 up) was important.
"When it clicks together, and you play those finals, and you’ve been playing those games all day long, the next time you come, you remember that."
Nijman continued: "Me and Jermaine will be close in the next few months, but this is a big step into the top 16, and hopefully there will be many more steps made.
"Top 16 was one of the goals I had at the start of the year, to get that privilege of starting on the Saturday (in Euro Tours) and starting on the left side of the draw in big majors."
Nijman opened with a 6-2 win over Scott Williams before edging past Tom Sykes after surviving a match dart. He then beat Sebastian Bialecki and Ryan Searle 6-3, followed by a 6-2 victory over Nathan Potter.
He produced his best display in the semi-finals, averaging 103.41 in a 7-4 win against Tom Bissell.
Wattimena made the stronger start in the final, but Nijman responded to lead 5-4 and moved ahead at 6-5 after an 80 checkout from his opponent. Wattimena missed six darts at double to level, allowing Nijman to take control before closing out the match in 14 darts.
Wattimena, playing in his first final of the year, had earlier beaten Martijn Dragt, Sietse Lap, Joe Hunt and Tommy Lishman. He then averaged 104.43 in a quarter-final win over Chris Dobey and defeated Kevin Doets 7-3 in the semi-finals.
Results
Last 16
Wessel Nijman 6-3 Ryan Searle
Nathan Potter 6-2 James Wade
Tom Bissell 6-0 Beau Greaves
Max Hopp 6-5 Darryl Pilgrim
Chris Dobey 6-1 Chris Landman
Jermaine Wattimena 6-2 Tommy Lishman
Kevin Doets 6-5 Mike De Decker
Gary Anderson 6-3 Alexander Merkx
Quarter-finals
Wessel Nijman 6-2 Nathan Potter
Tom Bissell 6-3 Max Hopp
Jermaine Wattimena 6-3 Chris Dobey
Kevin Doets 6-1 Gary Anderson
Semi-finals
Wessel Nijman 7-4 Tom Bissell
Jermaine Wattimena 7-3 Kevin Doets
Final
Wessel Nijman 8-5 Jermaine Wattimena