The Milton Keynes Lions reached only the second final in their history when they beat BBL Cup holders Guildford 91-80 to reach January's final.
Yorick Williams hit 26 points, including two vital third-quarter three-pointers, as the Lions held on to end the Heat's reign.
Newcastle Eagles reached their eighth major final in four seasons when they edged out the Scottish Rocks 75-69.
Charles Smith led the Eagles' scoring with a game-high 20 points.
Newcastle led just 71-67 with 1:21 remaining, but the Rocks could get no closer, missing out on their fourth Cup final in five seasons.
Maurice Hampton scored 15 points for the Rocks and Moritz Wohlers added 14. Lynard Stewart and skipper Andrew Bridge each scored 16 points for the Eagles.
A series of scoring streaks by Milton Keynes kept Guildford at bay in the second semi-final. In the first half, they hit a 19-4 streak to lead by 12 points at half-time.
After Guildford drew level in the third quarter, Williams and Tony Windless combined for three successive three-pointers in an 11-2 run.
With three minutes remaining, an 8-0 streak gave the Lions an 89-77 lead and killed the game off, and Milton Keynes reached their first final since 2002 in the process.
Michael New scored 21 points for the Lions, while Tony Dorsey had 20 points to lead Guildford's effort.