The Cumbrian got the better of Patryk Pientnik in Manchester.
Sewell delivered the decisive blow in the second round as he won his bantamweight fight by knockout.
The Carlisle fighter went on the attack with just over 30 seconds left in the second round.
A powerful right and left-hand combination sent Pientnik, a fellow debutant from Poland, to the canvas.
Sewell’s opponent got unsteadily to his feet amid referee Alan Jackson’s count but the fight was swiftly declared over.
The first round had seen Sewell – nicknamed ‘the Scumbag’ – land an early right hook that had Pientnik wobbling, before the Carlisle boxer connected with another powerful left-hand shot as the fighters traded early blows.
It was a first fight for Sewell (right) since being signed to the BKFC (Image: BKFC)
Pientnik survived the first round but the Cumbrian’s salvo in the second round earned him victory at BKFC 81 Manchester, with the fight taking place at the AO Arena.
Sewell was signed by the high-profile BKFC platform this summer after impressing in early bare-knuckle bouts.
He has been working with fellow Cumbrians such as Danny Christie, Carlisle’s former BKFC British champion, and top west Cumbrian coach Arron Adair.