After showing off the pink ball to the Adelaide crowd following his fifth scalp, cricket commentators on Reddit spotted a message the star quick had written on his arm band.
The message was revealed to read: "F... it. Bowl fast".
When asked about his mentality this summer after a disappointing Ashes campaign this year, Starc said he is trying to keep himself focused on the simple joy of bowling heat.
"I've always tried to keep it simple through my cricket," Starc said after the day's play.
"I got in a really clear mindset after that first Shield game of the summer. Just tinkering with a few things and keeping it pretty simple and clear and doing a lot of work with (bowling coach) Andre (Adams) back in NSW to get those really positive feelings and clear mindset. And it has seemed to pay off."
He also narrowly missed a hat-trick against the tourists. He claimed his fifth wicket when he had Babar Azam edging behind for 97, before trapping Shaheen Shah Afridi lbw for a golden duck.
He then caught the leading edge of Mohammad Abbas' bat the next ball before it flew away safely, denying Starc a rare piece of history.
Regardless, the haul continued his streak with the pink ball. His 32 scalps in six day-night Tests is 10 more than any other player, while Sunday marked his second five-wicket haul with the pink ball. He has also taken the most first-class wickets by an Australian in day-night matches, with his tally now at 58.
It is an amazing turn around for Starc.
He was beaten from pillar to post as he lost his rhythm last summer, only coming good for the final Test against a lacklustre Sri Lanka. He then only got one chance in the Ashes, a shock omission for all bar the Manchester Test and again dropped for the last at The Oval.
"How he didn't play that last test in the Ashes is beyond me," Aussie great Brendon Julian said on Sunday.
