At that stage he had passed all the on and off-field testing protocols but he gave an unsteady performance after returning to the crease and he woke up on Sunday morning reporting a headache and feelings of grogginess.
Follow-up tests showed his results had deteriorated and Cricket Australia became the first side to initiate the concussion substitute rules that were introduced by the International Cricket Council just this month, with Marnus Labuschagne the first such replacement.
Smith had argued against coming off in the immediate aftermath of the blow and was eager to return as soon as possible but had no complaints about being pulled from the match once his condition became clear.
"I woke up feeling a little bit groggy and with a headache again, I had some tests done and upon further assessment it was deemed to be a mild concussion unfortunately," he told CA.
"The results changed slightly, they declined a little bit. With the tests I've done and how I've woken up, it's the right decision.
"I'd love to be out there trying to keep performing and trying to help Australia to win another Test match but the right decision has been made and I'll be monitored very closely for the next few days."
It is just five years since Smith's friend and team-mate Phil Hughes died after being hit by a bouncer in a Sheffield Shield match and, although CA has undoubtedly led the way on head injuries and concussion substitutes, questions will be asked over whether or not Smith should have been allowed to bat again.
Having passed both computerised and non-computerised assessments, Australia doctor Richard Saw saw no reason to step in but it is now apparent that Smith was in a vulnerable position and would have been prone to further damage had he been hit again.
That made it all the more surprising to hear he is intending to prove his fitness for the third Test in Leeds, which begins just four days after his diagnosis.
"It's obviously a quick turnaround between Test matches and I'm going to be assessed over the next five or six days, each day probably a couple of times., to see how I'm feeling and progressing," he said.
"Hopefully I will be available for that Test match. It's up to the medical staff and we'll have conversations...it's certainly an area of concern, concussion, and I want to be 100 per cent fit.
"I have to be able to train probably a couple of days out and then face fast bowling to make sure my reaction time and all that kind of stuff is in place - there are a few tests I have to tick off and time will tell."
Smith's optimism does not appear to be shared by the governing body, with a statement from CA casting doubt on his appearance.
"In terms of Steve's availability for the third Test, this will be considered over the coming days but the short turnaround to the next Test is not in his favour. Steve's fitness will be assessed on an ongoing basis," it read.
CA guidelines rule out any return to physical activity for 24 hours, after which it must be a graduated process taken under constant review.
The ICC's most recent review on the subject recommends a week away from action and the England and Wales Cricket Board does not allow for a return to full training before at least six days have passed.
More encouragingly, Smith appears ready to try wearing a protective stem guard again - the extra layer of neck protection introduced following the Hughes tragedy but shunned by some players as being uncomfortable.
"That is certainly something I need to have a look at and perhaps try in the nets and see if I can find a way to get comfortable with it," said Smith.
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