Much of the pre-game talk had surrounded the two California-based teams' wildly different approaches for navigating the epic flight and 17-hour time zone difference to Melbourne and its iconic 100,000-capacity cricket stadium. The Rams had jetted in just the morning before.
How far that affected the game will be debated. But reigning MVP quarterback Matthew Stafford and star off-season acquisition Myles Garrett undoubtedly looked sluggish up against their San Francisco counterparts, who arrived a week earlier to acclimatize.
Purdy put on a clinical performance, shrugging off a poor early interception to find Demarcus Robinson with a 39-yard touchdown pass, before finding the dangerous Mike Evans and Deebo Samuel Jr in the end zone to seize the game.
"Just so proud of this team. Hey, we embraced going to Australia - 15-hour flight, we're here the whole week. It was a grind, but we did it," said 49ers tight end George Kittle.
The Rams entered this new NFL season as the clear favorites to win a Super Bowl being held at their SoFi Stadium home in Los Angeles in February, with a formidable defense bolstered by Garrett.
But the giant 100,021 crowd packing into the Melbourne Cricket Ground - the seventh-biggest ever for a regular-season NFL game, despite an unusual morning kickoff time to accommodate US television audiences - skewed toward San Francisco.
"I love when they (Rams) came out and they were booing. We was out here for a week. We enjoyed the city. I don't think you can fly 16 hours and be ready to play," 49ers receiver Samuel told Australia's Channel Seven.
And the Niners started brightly, swiftly forcing a Rams punt and then driving to the red zone and taking an early field goal.
The Rams briefly sparked to life with Matthew Stafford's 41-yard pass to Puka Nacua.
At 2nd & goal, Stafford handed the ball to Kyren Williams, and the running back sprinted through the heart of the Niners' defensive line for touchdown.
Purdy then threw a poor pass that was easily intercepted by Quentin Lake, prompting the Rams defense to pull out a "jet lag" celebration, lying down and pretending to nap in the endzone.
The Niners did not seem to appreciate the taunt. Renardo Green snaffled an interception off Stafford, and a long drive resulted in a Demarcus Robinson touchdown from a 39-yard Purdy sling.
'No excuses'
It meant San Francisco took a slender lead into halftime, as play paused for a Jonas Brothers concert on a game broadcast globally by Netflix.
San Francisco immediately picked up where they left off, some powerful running by Christian McCaffrey taking them back to the red zone.
Evans - the veteran receiver acquired from Tampa Bay this summer, and a constant dangerous target in the first half - grabbed a short touchdown pass for 17-7.
Another long pass to Nacua advanced the Rams, who reached 1st & goal, but they could not convert the critical chance and yielded a turnover on downs after a resolute 49ers goal-line stop.
In the ensuing 99-yard San Francisco drive Samuel grabbed a third touchdown pass from Purdy, who paused and scrambled to his right before picking out his man for 27-7.
With barely three minutes remaining, Stafford was strategically withdrawn by coach Sean McVay. The Rams' attention swiftly turned to the flight home.
"I make no excuses. Whether you want to say it's about travel, whatever. We just weren't good enough," said McVay.
"I didn't coach good enough, and we'll look at it and we'll move forward."