Describing Saturday's Olympic Stadium showdown as the biggest moment in the career of every member of the touring party, Rowntree was not about to give an inch in the final few hours of the pre-match psychological battle.
Gone was his normal easy conversational style and the former England prop was all business as he brusquely rebutted any negative stories attaching themselves to the Lions this week.
First up were the Twitter rumours that replacement centre Manu Tuilagi had suffered an injury and Ireland's Brian O'Driscoll was in line for a dramatic return to the team he was controversially omitted from on Wednesday.
"News to me. We're all good. Trained well this morning," he said with a breezy harrumph that set the tone for the remainder of the news conference at North Sydney Oval.
O'Driscoll, he said, had been "exemplary" since being axed, ending that line of questioning by describing it as "Wednesday's story".
The two days off in the Queensland resort of Noosa earlier in the week, also criticised by some, were important to allow the team to "switch off" after the second Test defeat and had "refreshed" the team.
The record-equalling selection of 10 Welshman in the starting XV was justified on form, he added, and the beefed up pack was "appropriate" for the match - even if the Australians should not read too much into it.
Rowntree continued the tourists' courtship of the referees over the last two Tests, describing Frenchman Romain Poite as "one of the best referees we've got up north" and even offering the assistance of his players in officiating the scrum.
"He's known for his setpiece accuracy, so I'm looking forward to working with him tomorrow night," he said.
"We've got a real responsibility to help the referee at scrum time.
"Indeed, following on from last week and the week before, all we can do as a group is work on what we're showing the referee and what we're doing technically.
"And try to improve that and try to take the referee out of the equation so to speak."
Hooker Richard Hibbard, brought into the starting line-up for his bulk, later articulated the open secret that the Lions were planning to attack the Wallabies in "the scrum, breakdown and physicality".
For Rowntree, though, that would have been giving away too much to the enemy, although he was happier to discuss the possible weaknesses in the home side's preparations.
The surprise recall of flanker George Smith after four years out of Test rugby and six weeks on the sidelines with a knee injury was a "surprise", he said, and it would be interesting to see how match-fit the 32-year-old was.
Rowntree also expanded on a theme introduced by head coach Warren Gatland earlier in the week, that the Wallabies had expended a huge amount of emotion in winning last week's second Test in Melbourne to level up the series.
The question, Gatland suggested, was whether they could summon up similar intensity for a second week in a row against a Lions team at desperation point as they bid to win a first Test series since 1997.
"I thought we saw the reaction from Australia after they beat us, especially their captain, (James) Horwill, who was crying after the game," Rowntree said.
"They threw everything at us in that game, and beat us by a point. We really didn't get our game going.
"There's loads more to come from us. The guys are desperate to win. This is grand final rugby, last throw of the dice. Everything to play for.
"These players are desperate for tomorrow."
- Sports & Recreation