He admits to it being a "baptism of fire" but the 24-year-old carried himself like a seasoned international, producing a dynamic display in the loose and at set piece time.
After a few days away from the Irish camp, playing cards mostly and attending Leinster's Magners League win over Cardiff Blues in his civvies, Heaslip's focus is fully on next Saturday's Scotland game. Although he is modest enough to not consider himself a certain starters.
"Oh God no, not at all. Every time someone asks 'can you get tickets for the Scotland game?' I've been saying 'you can hold off. I will find out on Tuesday if I'm playing and then let you know'," Heaslip replied when asked if he is confident of holding onto the number 8 jersey.
"I won't have a clue until the morning and I think that's the same for a lot of guys."
Heaslip said it was a surreal experience to be down at the RDS watching on as Leinster beat the Blues on Saturday night and retained their lead at the top of the Magners League.
"It was a first, the first time I've done it (in the civvies as an Ireland squad member). It was a bit weird alright but I still robbed a couple of sandwiches afterwards!
"It was freezing down there. It was good though. Leinster didn't start too good and gave themselves a minus 14 handicap and I'm sure a couple of people put bets down then and won some money, but it was a good, hard-fought win by the lads.
"It was not great in the first half but in the second half they were good, they kept the ball well and stuff like that.
"I was in the changing room afterwards and the lads were very happy to have stretched out the lead," he added.
"We have got to keep ourselves competitive. Maybe not this year but during the November internationals when players are away, and the Six Nations, those games are almost more important than some other games in the Magners League.
"It's just a great win for the lads, especially against Cardiff who were second in the table. Now we're clear by six points which gives us a bit of a buffer zone."
Heaslip has had a big role in helping Leinster hit the summit. Indeed he is the fourth top try scorer in this season's league and his experience in the competition means he is pretty familiar with Scotland's back row collective.
"The Scots have a pretty dynamic back row with some good ball carriers and they also play the game with a lot of width," explained the Naas native.
"They have some good speed on the wings. We are going to have our work cut out for us. The coaches have obviously sat down and looked at what they want to do and that's what we're going to start doing today and for the rest of the week."
A win over Scotland would keep Ireland in the championship race and be the first piece of another Triple Crown jigsaw. Heaslip and company are eager to cut out the errors that cost them so dearly against France.
"At the moment, we're just concentrating on correcting some errors - defensive errors and stuff like that that we made in the last game.
"Our tactics were sound, which we proved with the end to the game. I just think we made a couple of errors and that was it," he added.
"A couple of tries they got from being really smart and quick from turnover ball - the chip to the corner and (Vincent) Clerc just ran on to the ball.
"They got a bit of luck as well with the bounce of the ball. It was a mix of all things but, in total, we were happy with the performance but not happy we lost.
"Now we're making sure we're fully prepared for the Scotland game and don't make the same mistakes twice."