Both players were involved in long baseline rallies during the game and it took some invention to win points with drop shots and winners from acute angles being the order of the day.
Berrettini seemed to be in control at 4-3 in the opening set but Krajinovic only needed to convert one break point to take advantage and eventually clinch the set on serve.
However, the Italian bounced back in the second and served much better than his opponent to get back into the contest.
Krajinovic managed to save four break points but, as in the first set, only one break point conversion was needed to settle scores.
Berrettini then broke the Serbian in the very first game of the final set and took a 2-0 lead. A shaken Krajinovic did not recover and the 23-year-old Italian went on to convert three of four break points to win the match.
Berrettini, who is yet to lose in an ATP final, made it two years in a row where an Italian has won the event after Marco Cecchinato won it last year.
(Reporting by Rohith Nair in Bengaluru, editing by Pritha Sarkar)
