Could this be the one?
Canada's Auger-Aliassime, on the other hand, is still waiting for his first senior career title and was never really in the contest as Monfils ended the week without dropping a set.
This was the first meeting between the two players on-tour.
Monfils stylishly got the better of an apparently defeated Auger-Aliassime at the net to tee up another three openings, taking the last of them.
Carreno Busta beat Italian Jannik Sinner 7-5 3-6 7-6 (8-6) while Auger-Aliassime overcame Slovenia's Aljaz Bedene 6-4 7-6 (8-6).
Following a brief Monfils scare, Auger-Aliassime went long when defending a third break opportunity next time out and slipped further behind, allowing the third seed to serve out the opener.
Carreno Busta won the next game on-serve to ensure the set would be decided by a tiebreaker.
Earlier, Nicolas Mahut and Pierre-Hugues Herbert of France posted a 7-6 (5), 4-6, 10-7 win over Finland's Henri Kontinen and Germany's Jan-Lennard Struff in the men's doubles final.
Auger-Aliassime is searching for his first career ATP Tour title.
The youngster kicked off the action with an ace, fending off three break chances in the third game to stay on the positive side of the scoreboard until game five when Monfils grabbed four straight points on the return to move in front after a backhand victor. En route to winning the second set 6-4, the teenager won 95% of his first service points and had seven aces.
Making a slow start last week, Gael claimed 18 sets in a row, earning his tenth ATP crown in Rotterdam following a 6-2, 6-4 victory over Felix Auger-Aliassime in an hour and 26 minutes. Krajinovic, ranked No. 39, and Monfils, ranked No. 9, take to the court later this afternoon.