The pre-round first and second on the leaderboard had made a sleepy start and the charging field were all over them.
Cue carnage from the Spanish-Australian duo.
"We were both even-par through four and a combined 21-under-par in the next 14 holes," gasped Rahm, adding rather humbly: "It's this golf course, right?"
Smith birdied five of his next seven holes and then each of the last four to complete a second consecutive 64 for a 54-hole total of 26-under 193.
Rahm equalled that tally for the week with a dazzling display that edged Smith in both those spells and also on the day: he birdied six of the next seven holes, his final burst witnessed four birdies and an eagle-3 in the final five holes, and his total for the circuit was a 12-under 61.
"Watching Jon was pretty intense there on that back nine," Smith said afterwards. "It was some of the best golf I think I've ever seen, definitely some of the best putting."
Rahm explained how he made a couple of early putts that he'd left short on Friday.
"It gave me so much confidence I just kept going," he said. "Got right on the birdie train. It's definitely doable on this golf course, but you still have to hit the shots and tomorrow we've got to keep doing the same thing.
"We had a fun battle today and I'm guessing tomorrow's going to be more of the same. We're going to need a lot of birdies to get the win.
"We fed off each other, right? I had three shots to make up today and (Cameron) wasn't making it easy. I stood on the tee at 14 thinking, 'Well, he's probably going to birdie 14 and 15 and have good looks at 16, 17 and 18, so I've got to do the same thing."
"I wouldn't be surprised if there's another 61 or 62 out there tomorrow," Smith concluded. "Need to keep playing good golf."
The pair have set a new 54-hole record total for the course and now look ready to end a long period of dominance for American golfers in the tournament.
There were nine straight international wins from 2002 through 2010, but every year since has witnessed a home champion.
If that record is to be maintained Daniel Berger, currently solo third, needs to overhaul to the top two from five back on 21-under 198 after three 66s. Matt Jones (Australia), Sungjae Im (Korea) and Patrick Cantlay (USA) share fourth on 20-under 199.
It looks very much like a two-horse race. Let's take a closer look.
Smith from this position
"It's what I love," he said after his third round. "I love to compete. More so than missing golf I just missed competing over the break. It's great to be out here and in the hunt on the weekend."
This is a sixth career 54-hole lead for Smith and in his first two he claimed a pair of wins. On the PGA Tour - and in an individual event - it's just his second lead however. In the previous instance, at last year's The Northern Trust, he finished second.
He's a past winner in Hawaii - at Waialae in the Sony Open - and said: "Hawaii reminds me so much of where I grew up, it's insane. The grass that we hit off, the greens being quite slow and grainy. It's awesome, I love it here."
Rahm from this position
Rahm is 5-for-9 at converting a 54-hole lead into a win throughout his career (although he would surely have improved that when six clear in the 2021 Memorial before being forced to withdraw).
He said of Sunday's task: "What I've got to keep doing is just keep hitting it as well as I am tee to green. Keep putting it in the fairway and keep hitting good iron shots, give myself plenty of looks, and some of them will go in. You can get hot on this golf course and hopefully I can do the same thing tomorrow."
In his fifth start at the course, Rahm has never ended the week outside the top 10 and now has the chance to improve on his previous best finish (second in 2018).
Plantation winners stats
15 of the last 16 winners of this tournament were within two shots of the lead at this stage. The exception was five blows back which gives Daniel Berger a very slight sniff of catching the two pace-setters.
The Putting Average of the last five winners reads: second, second, first, first, first. The current top six on the leaderboard are all ranked seventh or better in that category through 54 holes so the trend is on track to continue. Smith leads the field, but Rahm did so in round three and a repeat of that brilliant putting would improve on his current ranking of fifth.
Any hope for the chasers? Well, back at The Northern Trust last August the same two players were tied for the lead at this stage and Tony Finau passed them (but he had started the day just two shots back).