Australia's Tomic won 7-6 (7-5) 3-6 7-6 (7-4) in Bogata to claim his first tournament victory since January 2013 when he won the Sydney International.
In a tough final at the ATP 250 event, which was completed in two hours and 16 minutes, Tomic's questionable temperament was put to the test on a number of occasions and the 21-year-old battled through admirably, no less so than in the closing stages of the match.
Tomic led 6-5 in the third set and had a championship point at 30-40 in Karlovic's sixth service game only for the Croatian veteran to avoid defeat with a second-serve ace down the middle, which prompted a wry smile from the Australian.
After claiming advantage on the first deuce point, Tomic then watched Karlovic send down yet another ace before the reigning champion forced his way to a tie-breaker.
But just like in the first set, Tomic took control of the tie-breaker with an early win on his opponent's serve, winning the first two points and although Karlovic levelled at 2-2, the Australian claimed five of the next seven, including two on return, to lift the trophy.
Tomic worked hard to exploit Karlovic's second serve, winning 52 per cent of points when the 35-year-old missed his first serve.
Unsurprisingly, Karlovic had a lot of joy with his serve, notching 39 aces and winning 88 per cent of points on his first serve, as Tomic failed to break the world number 29.
In the first set, all games went to serve, ensuring a tie-breaker was required.
Tomic notched the first point on serve and then stunned Karlovic on his second service point, before racing away to a 4-1 lead.
Karlovic responded but could not reel in the world number 124, who will break back into the top 100 following his victory in Colombia.
In the second set, Karlovic claimed the only break of serve for the match, winning the eighth game before levelling the contest at a set apiece, but he could not hold on in the third, as Tomic emerged victorious from just his second ATP final of 2014.