At the Sailen Manna Stadium in Howrah, record 32-time winners Bengal took time to stamp their authority on the game but eventually ran out winners through goals from Jiten Murmu (57') and Tirthankar Sarkar (90+2').
Karnataka's Sukesh Leon hit the woodwork in the 17th minute and almost gave the tournament favourites an early scare but goalkeeper Ranajit Majumder showed intense resolve to keep his goal intact from the rebound.
The real fight started in the second half when Sumit Das' fierce effort was parried off by Karnataka keeper Shaikhan CP but Murmu, the former East Bengal man, was at the right place at right time to slot home from the rebound.
The momentum was with Bengal as they continued to dominate the game. Tirthankar Sarkar, formerly of Mohun Bagan, could have turned provider for Bidyasagar Singh who scuppered a chance with a quarter of an hour to go.
Sarkar sealed the game himself in injury time when he converted from a free-kick won by Murmu at the edge of the box to seal a spot in the final.
Meanwhile, at the Mohun Bagan ground, Kerala were dominated for most parts of the game by 2013/14 champions Mizoram but conceding a goal to substitute Afdal VK (54') flushed all their good work down the drain.
Both sides started off with caution and it was the north-eastern side that had three chances in the first half, all coming from the right flank, operated by former Aizawl FC man Lalbiakhlua. Lal Romawia, who had scored two braces in the group stages came close to breaking the deadlock but shot over past the half-hour mark.
Kerala head coach Satheevan Balan brought in Afdal VK in place of Sajith Poulose just before the half-time whistle, which turned out to be a masterstroke nine minutes after the restart.
Jithin MS broke from the right and played a square pass to Rahul KP who found the keeper through a first-time shot. The ball rebounded off the far post and Afdal showed an immense presence of mind to sneak in and slot home.
Mizoram, who had made nine changes from their last game, were without their head coach Lalsangzuala Hmar on the touchline who was serving a one-match suspension. Even after the goal, the team kept on creating some good chances but none of them was rewarded.
Kerala tightened their defence to see through the game and made their way to a 14th Santosh Trophy final. It will be a repeat of the 1993/94 final and a first for the five-time champions since 2012/13.
Hosts and defending champions Bengal will now face Kerala in the summit clash, to be played on 1 April at 2.30 PM at the Salt Lake Stadium.