Commenting on his first cap at this level, the 24-year-old Dubliner beamed: "(I'm) absolutely delighted to be honest. For myself personally, I went out to do my role. Thankfully it just came off well and the lads around me helped me really well too.
"It was very emotional. I was welling up a bit. There is nothing bad about that. During the anthems a bit and a few nice texts from family and friends was really nice.
"(Team-mates) were just saying play your game. You are here for a reason and it's the same as any other game. You need to focus and try and do a job.
"We just concentrated on the task in hand and thankfully we got a few penalties, but certain refs could have put it the other way. On the night I thought we went well as a pack."
McGrath said the Irish squad were simply happy to get the victory against a difficult Samoa side who failed to convert early chances, and the visitors then saw the game drift away from them as Peter O'Mahony touched down after an impressive driving maul.
"It is a great step forward for the team but it is back to brass tacks on Monday. We will just concentrate on the task in hand on Monday, work through the week and take it from there.
"(The slow start had) probably a lot to do with a lot of lads not having played together since Italy last season and trying to play a new way as well, but we definitely took a step (in our progression)."
New forwards coach John Plumtree said earlier in the week that a key area was correcting the errors which saw Ireland's lineout come undone at times last season.
McGrath was an important component in an improved set piece return yesterday and he felt that the work done in training was the reason for the turnaround.
However, the St. Mary's College clubman shrugged off suggestions that first choice loosehead Cian Healy will now need to look over his shoulder after his impressive debut.
"It was brilliant. We had done a lot of (set piece) work during the week. John (Plumtree) is a stickler for getting excited for jumpers and lifters in defensive and attacking lineouts," explained McGrath.
"I thought we worked really well during the week. We tried to get things sorted and thankfully it came off. I think a lot of video work during the week went into it (the scrum). It's Besty (Rory Best) and Rossy (Mike Ross) beside me, it's great and having the lads behind me.
"It's basically a lot of preparation, looking at the video and trying not to take a step back, try and go after them and showing people you should be there.
"(Myself and Cian) are good pals. We push each other well (at Leinster), we give each other tips. He's a great fella. I have the utmost respect for him.
"What Joe (Schmidt) does is his own business (in terms of team selection), but all I can do is perform and enjoy myself.
"I didn't think I played that well to be honest but I just went out to do a role, was a cog in the team and it just happened from there."
McGrath, who sported a 'shiner' after his on-field activities, was sweating more about his post-match duties as he was called upon to sing a song after the game - a time-honoured tradition that the new caps must endure.
"I just had to sing up in the O2 box. Drico (Brian O'Driscoll) and Paulie (O'Connell) hung me out to dry! To be fair I had practised a small bit because I am not a great singer. 'Piano Man', so it was simple enough and people can get into it.
"(The shiner) shows you were in the game a bit. I always like to get a few knocks but unfortunately it was my own player, Dev Toner. He's fairly lanky and awkward so a few lads have caught elbows and knees off him over the years!"