On the first night of this tour, Bairstow ventured to the Avenue bar in the suburbs of Perth and greeted Cameron Bancroft with a now notorious genial head-butt.
While it took a few weeks for the incident to come to light - Australia used it in the second innings of the first Test to unsettle Bairstow and some have subsequently suggested it provides evidence of England's "drinking culture" - it briefly threatened to disturb the focus of both Bairstow and the England camp.
But upon reaching his century here, Bairstow kissed and then gently head-butted his England helmet several times in a clear and good-natured reference to the episode. It was a celebration that demonstrated both an ability to laugh at his own errors and suggested the incident had long been put behind him. And, as he said afterwards, it may well be the whole affair gave him made him "more determined to succeed."
With that context and the fact that it had taken Bairstow until his fourth Ashes series, his 12th Ashes Test and his 20th Ashes innings to make his first Ashes century, it was perhaps not surprising that he rated it his "favourite" Test century.
"The hundred in many ways was my favourite one," Bairstow said. "I've played in a few Ashes series now and to score an Ashes hundred - something that had eluded me until now - is something you dream about as a kid. This is the pinnacle of the game.
"It means a heck of a lot to be involved in record stands. You want to make an Ashes hundred. You want to look back in the archives when you're retired and say to your kids or your grandkids: 'I made an Ashes hundred at the WACA'.
"There's a huge amount of pride that comes with any hundred and in playing for your country.
"The celebration was a bit of light hearted fun and it should be taken as such. It was spontaneous. I hadn't thought about it before.
"Hopefully it is a positive reaction I have given in this innings. Sometimes the chat out there spurs people on and makes them more determined to succeed."
Bairstow hadn't scored a Test century since an unbeaten 167 against Sri Lanka at Lord's in June 2016 - 21 Tests and 38 innings ago - though he made 99 against South Africa at Old Trafford in August. But here he posted a stand of 237 with Dawid Malan - a record for England's fifth-wicket in Ashes cricket - to steer England from the peril of 131 for 4 to the relative comfort of 368 for 4 before a now familiar batting collapse.
While Bairstow admitted the collapse was "frustrating" and the manner of Malan's dismissal "disappointing", he maintained a 'glass half-full' perspective.
"It was disappointing the way he got out," Bairstow said, "but the intent we showed in our batting was much better.
"Maybe we're frustrated in some ways, but it depends how you look at things. We were 100 for 4 at one stage. You can either think it was a fantastic recovery or you can look at it and say we've let our position slip."
Meanwhile the ECB confirmed Mark Wood would remain with the England squad after the end of the Lions tour on Sunday. There are currently no plans to retain the services of any of the other players in that squad, most of whom will arrive back in the UK on Monday.
That means that, despite the failings of the top-order, England's only obvious batting options for the final two Tests are Ben Foakes and Gary Ballance. While others are either in Australia or shortly will be - Jos Buttler, Jason Roy and Sam Billings are among those involved in the BBL while Sam Robson is spending time with his family in Sydney - there are currently no plans to utilise any of them in the Ashes.
It remains to be seen how much of a role Craig Overton will play in the rest of the match. Overton was forced off the pitch for a while on the second day after jarring a rib as he attempted to claim a tough caught and bowled opportunity. He returned to the field before the close and it was not deemed necessary to send him for a scan. But he will be assessed by the medical team before play on the third day to ascertain his fitness to bowl.