After a barren first session where NorthEast United dominated for long spells, Katsumi scored the all-important goal in the 54th minute.
The match was preceded by a colourful opening ceremony that saw over 500 performers including John Abraham, Sachin Tendulkar, Abhishek Bachchan, Mahendra Singh Dhoni, Aalia Bhatt, Varun Dhawan, Jacqueline Fernandez and Ranbir Kapoor perform on the stage.
Badminton star P.V. Sindhu, who took silver in the women's singles category at the Rio Olympics, was also present on the occasion.
NorthEast United were determined to get a positive result from the opener and fielded an attacking line-up with Nicolas Velez, Holicharan Narzary and Emiliano Alfaro in their forward line.
Kerala, on the other hand, were content in soaking up the pressure which they did well in the first 45 minutes but succumbed to NorthEast's might in the second session.
NorthEast United started the stronger of the two teams although there were hardly any chances in the opening minutes.
The home side got their first look at goal in the 24th minute, thanks to a sloppy pass by Kerala goalkeeper Graham Stack which was almost capitalised upon by Nicolas Velez. The lazy kick fell to Romaric who struck from a distance but had no power to beat and embarrass the rival goalkeeper.
A free-kick midway into the first session saw Velez out-jump his marker and head towards goal but Stack did well this time to stretch wide and keep out the danger.
NorthEast were continuously attacking in the opening 45 minutes but had nothing to show as the strikers were found wanting.
The hosts' defence was relaxed for most part of the first half but centre-backs Mailson Alves and Gustavo Lazzaretti were needed to stay alert whenever the three-man strike force of Kerala Blasters worked their way on top.
Two successive attempts in the 35th and 36th minutes were the closest they got but Antonio German's shot from about 30 yards fell into the safe hands of goalkeeper Subrata Paul and Sandesh Jhingan could not direct his header towards goal.
After near misses in the first half, NorthEast United finally tasted success early in the second session. It was Velez who made it happen after dancing down the left flank and essaying a cross which the Kerala defence missed and Katsumi was only too happy to speed forward and tap it into the goal.
Kerala Blasters tried hard to find the equaliser and came close just after the hour mark.
Jhingan's attempted cross sailed unintentionally towards goal and Subrata Paul dived frenetically to keep the ball away from danger. From the resultant corner kick, Subrata left his charge needlessly, got stranded but German's strike from close range missed the target by a whisker.