"Hopefully people out there have seen we've got some really good quality youngsters coming through and that the future's bright if we look after them," said Hay.
Suburbs finished second during the regular season, two places above Wellington, but the capital side did the double over Hay's team and boasted far more grand final experience, having reached the last four, winning in 2016 and 2017.
But Hay's slew of young stars showed little sign of nerves, with McCowatt at the centre of most of his team's best attacks. He, Elijah Just and Andre de Jong caused Wellington's back three plenty of problems throughout the 90 minutes.
The win also secured Suburbs a place in next season's Oceania Champions League for the first time alongside minor premiers Auckland City.
The Lily Whites got off to a great start, taking the lead after seven minutes. Dalton Wilkins produced an audacious flick to lift the ball over a defender in the penalty area and find an overlapping McCowatt.
He struck a left-foot volley across the face of goal which was deflected in for an own goal to put the Auckland club ahead.
While the television commentators attempted to attribute the opening goal to McCowatt — a claim which raised even McCowatt's eyebrows in his post-match interview — there was no doubt the second was all his. He curled a perfectly-placed right-foot shot into the top corner to put Suburbs two up and in total control 10 minutes before halftime.
Wellington grew into the game but failed to register a single shot in the first half.
Around 10 minutes into the second spell, McCowatt netted his second, running at the opposition defence before unleashing a left-foot shot that left Wellington requiring a minor miracle to avoid defeat.
Just before the third goal, Wellington midfielder and former All White Aaron Clapham was stretchered off after a sickening collision which saw him suffer an accidental knee to the head from de Jong after sliding in to make a tackle. He soon regained consciousness and was taken to hospital for treatment.
McCowatt received the Steve Sumner Trophy as player of the final for the second consecutive season after scoring the only goal in Auckland City's 1-0 win over Wellington in last year's final.
Eastern Suburbs 3 (Own goal 7, Callum McCowatt 36, 57)
Team Wellington 0
Halftime: 2-0.
