Derby earned their spot by doing what few have done in recent years in beating the visiting holders Solent Kestrels 92-77.
It's the first time the Kestrels have missed out on making an NBL final since 2018/19, though there is still plenty to play for in other competitions this season.
Newcastle are finalists courtesy of a hard-fought home 92-88 home win over Reading Rockets.
The pair will face off at Sheffield's Ponds Forge on 2 January.
The Trailblazers' Sunday win was all the more stunning as they were 17 points down (51-34) at half-time. They turned the tables in remarkable fashion after the break, holding their illustrious visitors to just six third-quarter points, while pouring in 35 of their own to set up a big victory.
Blake Bowman led the Blazers with 22, Malcom Smith hit 21, while Rahemm May-Thompson had 15 and Ray Bruggeman scored 13 and dished out 10 assists.
Cole Gentry and Orlan Jackman paced the off-key Kestrels - who fell to Hemel Storm in league action the day before - with 19 apiece.
Newcastle had already knocked off Reading on Saturday with Brendan Federici and Martyn Gayle both playing the full 40 minutes to chip in 26 and 24 points respectively.
They also had to come from behind, with Rockets - led by Tyler Cartainio's 25 points and 15 rebounds - holding a 56-43 half-time advantage.
But Newcastle got the job done after the break, stemming their opponents' scoring, to seal their final spot.
The final will take place at Sheffield's Ponds Forge on Sunday, 2 January (12pm) ahead of the BBL clash between Sharks and Leicester Riders.
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Main image: Lauren Newman
Main image credit - Lauren Newham