Thrilled to win his first international cap, he said: "It's been a moment I've been looking forward to for my whole rugby career, I've always wanted to play professional rugby and to get there and get a cap under the belt is special for me, especially because it is with such a special team.
"Standing and singing the anthem was a moment I'll never forget. It's been a long week, I'm now glad it's over and that we got the win."
Diack lined out at blindside flanker and seemed to revel in the physical nature of the clash at Estadio Centenario, tackling and carrying strongly and also featuring prominently as a lineout jumper.
"I was happy with aspects of my game, but there are definitely things I'll have to work on. I thought in defence I could have worked harder at times," he admitted.
"I'm still very happy. To get my first cap, to get 80 minutes and the win it's a day I will never forget and I just want to cherish it."
When giving his reaction afterwards, Joe Schmidt singled out Diack for his 'hard work in the first half' and the 28-year-old, who has played for Emerging Ireland and the Wolfhounds in the last 12 months, will hope for more game-time in next weekend's second Test.
Schmidt was also pleased with the contribution of industrious centre Darren Cave as the post-Brian O'Driscoll era began with the Ulsterman in the number 13 jersey.
Cave made a terrific midfield break early on and was inches away from scoring a try in the final quarter, just putting a foot in touch under pressure from Tomas Cubelli as he touched down in the left corner.
It was a sixth Ireland cap and fifth start for the Holywood native, but those appearances have been spread out over five years - he made his debut on the 2009 summer tour - and his determination to nail down a regular starting spot is obvious.
In assessing his efforts as part of an all-Ulster centre partnership with Luke Marshall, Cave said: "I'm pretty chuffed with how it went. I got my hands on the ball early, which was good. To be honest it's left me wanting more. I made a couple of small mistakes, as did everyone, and it just leaves me wanting to play next week."
With the Pumas fielding a largely domestic-based team, there was a degree of unfamiliarity that Cave and company had to cope with as they prepared for the tour opener.
"When I first saw the list of Argentinian players on the plane I didn't know a lot of them. Joe has hammered us with the individual player profiles all week and I've been very impressed, particularly with club rugby in Argentina, which I would have known absolutely nothing about. I've been very impressed with the standard."
Having played his first international since last year's North American tour, the 27-year-old wants to retain his starting jersey and help Ireland see out a 2-0 series win.
"I was sucking diesel a wee bit if I'm honest, having not played in a couple of weeks and it being a bit humid and a bit warm. But, as I said, it's just left me wanting more."
The Irish touring party have flown back to Buenos Aires ahead of the second Test in Tucumán, for which some personnel changes are anticipated.
Head coach Schmidt said: "We'd expect that there will be changes. We'll have a look at who came through today over the next 48 hours.
"We won't do a lot tomorrow (Sunday), a little recovery and back to Buenos Aires. We'll try and make some decisions on Wednesday."
Half-backs Conor Murray (dead leg) and Jonathan Sexton (tight quad muscle) picked up injuries during the three-try victory in Resistencia. The strapping applied to Murray's left leg was precautionary.