As well as preparing to play, the Tongan had to practise to make sure he remembered all the words to lead the traditional war dance.
"I was just trying to remember the words as I was saying the Sipi Tau," Olakau'atu told AAP.
"It's a lot of emotions going through your mind, and just the adrenalin rushing through your body ... but it was more so just trying not to forget the words and taking my time."
Olakau'atu's stirring rendition of the Sipi Tau was the curtain-raiser to the Pacific nation's dominant 30-12 victory over England in Perth on Saturday.
The six-foot-five (196cm) giant was approached by co-captains Jason Taumalolo and Addin Fonua-Blake on day two of Tonga's pre-tournament camp to lead the traditional war dance before their World Cup matches.
The Manly forward isn't sure why he was chosen, especially with no experience, but felt incredibly honoured by the selection.
"Addin and Jason came up to me and it wasn't really an offer, it was more like a tell me to do it," Olakau'atu said.
"Especially coming from them, it's a such a huge privilege to get to lead it.
"Very proud experience, not only for me, but for my family as well, especially Mum and Dad."
The responsibility of the moment weighed on the now nine-capped Tongan before the match - he was brought to tears while belting out the national anthem.
"It's very emotional when you get to sing your national anthem ... playing for your family and country and faith," the barn-storming back-rower said.
His tears continued after a monster match, playing all 80 minutes and scoring two tries.
However, Olakau'atu hopes to improve on his pre-game performance of the Sipi Tau when Tonga play Lebanon on Friday.
"I'll go again in game two, and this time hopefully I'll do it with a bit more enthusiasm and a lot more emotion," he said.
"I got a lot of positive feedback from the boys in the squad, so as long as they're happy, that's all that matters."
Olakau'atu's 80-minute performance against England was several years in the making.
After dominating recent seasons at NRL level with Manly, and having made three State of Origin appearances for New South Wales off the bench, he was thrilled for a chance to play an entire match for his nation in his preferred position.
"Just a lot of gratitude towards the coaching staff and Woolfey (coach Kristian Woolf) for believing in me and trusting me to fulfil that position and play the full 80," Olakau'atu said.
"There were a couple of times in the game where it was very hard and we were on the back foot.
"And just going off my experience with an Origin campaign, you get that second wind a bit earlier and back yourself a bit more with a lot more confidence."
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