The victory secured the Irish a place among the second tier of seeds for next week's draw for the 2015 World Cup.
"This was my first cap and then there was the rankings issue on top of that, so it was a huge game for Ireland.
"I was more nervous than I'd ever been but messages of support from family and friends helped me settle," said Gilroy.
The 21-year-old ran in a try and helped create three more on his Test debut, employing a formidable combination of grace and power to torment the Pumas' defence throughout.
The Ulster winger was the star of a seven-try rout of opposition famed for their belligerence.
Ireland 46-24 Argentina - highlights
The success also ended a five-Test losing streak and afforded embattled coach Declan Kidney some breathing space.
Against a backdrop of high pressure and missing the spine of their team to injury, Ireland produced their best performance since humbling Australia at last year's World Cup and the magnitude of the occasion dawned on Gilroy as he battled to keep his pre-match anxiety in check.
He said: "I was extremely nervous but the messages I received told me not to put any more pressure on yourself, just be yourself and enjoy it.
"That's what I did and it was those messages from friends and family that settled the nerves."
The tension Gilroy felt was well hidden as he made the smoothest of transitions to Test rugby.
Just 10 minutes into the game he highlighted his finishing ability, taking an inside pass from Jonathan Sexton, sliding between two tacklers and evading three more for an outstanding try.
It set the tone for the rest of the afternoon as Ireland's most dangerous runner flourished amid a feeble defensive effort from Argentina, who were playing their 12th Test since June.
The strength of the performance earned comparisons with famous Irish wingers Simon Geoghegan and Denis Hickie and even identified him as a potential candidate for next summer's British & Irish Lions tour to Australia.
Kidney praises the performance of his young players against Argentina
"I was eager to take my chance because who knows when it will come again," added Gilroy.
"Past players said your first cap is special, just enjoy it. They said it just flies by and it does, but there are also moments I won't forget.
"It felt surreal. I couldn't believe I was there. Once you've had a taste of it you want more.
"This is a big confidence boost and, while I can't get ahead of myself, it's good to know I can perform at this level."
Gilroy had scored five tries for Ireland against the Barbarians in June and Fiji last week, but both games were non-cap internationals.
Kidney, whose future was in doubt, was not peddling his usual line in humility when he declared "you never in your wildest dreams think you'll score that number of tries against Argentina".
Everything Ireland tried came off with Sexton imperious at fly-half and Tommy Bowe poaching two tries, while Richardt Strauss and Simon Zebo also crossed the Argentinian line.
Argentina were abysmal, however, obliterated in every department of match that had end of season stamped all over it, although captain Juan Martin Fernandez Lobbe refused to use fatigue as an excuse.
"Now we must spend six months without seeing each other again. It's not what we wanted," he said.
"We had a good week and were fresh for this match. We've improved over the year but this is a sad way to finish."
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