There are times in sport when fate, kismet or just their own high quality performances demands that two players become rivals.
They find themselves contending in the same tournaments, their decisions are eerily linked, their sporting lives oddly entwined, controversy seems drawn to their tussle.
The pair of them emerged from extended winter hibernations to card 7-under-par 66s in round one of the Sentry Tournament of Champion, one shot behind the pace-setter Cameron Smith and alongside Daniel Berger, setting up a second round two-ball pairing which will extend this peculiar little narrative.
It began at the Memorial Tournament in June, when Rahm led the field by six after 54 holes, but was informed as he left the final green that he had returned a positive Covid test and needed to pull out of the event.
Next day Cantlay pounced. A Sunday watching Rahm's coronation was transformed into a head-to-head with Collin Morikawa in which the Californian emerged triumphant.
Two weeks later Rahm, believing karma was on his side, returned to action and won the US Open, his first Major Championship.
Later in the season Cantlay added victory in the BMW Championship and with it entered the Tour Championship with the field trailing him on added strokes.
Rahm's 72-hole total that week was the joint lowest, but Cantlay lifted the trophy, the FedExCup and the $15million bounty that went with it.
A fortnight afterwards they scored three and a half points apiece in the Ryder Cup.
Split at the polls
The PGA Tour membership was divided on who deserved to be anointed Player of the Year. Cantlay edged it, Rahm narrowed his eyes and said the right words through gritted teeth.
Then both of them decided they needed time away from the golf course. Cantlay took 100 days off, Rahm about half of that.
The question was how the FedExCup champion and the World No. 1 would emerge from that break. The answer was: very well.
"You can always expect a little bit of rust," Rahm said after closing with four birdies in his final six holes.
"But although I took time off, I wasn't on the couch, right, doing nothing. I was still working out. I was still practising as if I was still in the season.
"I took maybe three weeks off, which were very needed, but I was practising.
"So, again, I'm not that surprised that I played good, but it's really good to come out and start the year off the right way."
Cantlay's finishing run was even more impressive than Rahm's with four birdies and an eagle-3 in that final third.
He was also more willing to acknowledge that he was grinding through the gears early on.
"I still think I'm a little rusty and I saw that in my start," he said. "I got away with a couple of loose swings and one flier on the sixth hole where I was able to make a par, but maybe shouldn't have.
"I then hit a lot of quality shots and (the good run) had been a little time coming, it felt, because I made so many pars on the first 12 holes or so.
"That's just this golf course. Sometimes you can get on a little bit of a roll and start to make some birdies."
Golfers of every ability are aware that the return to the course after a hiatus can reap remarkably good rewards. Often the real test comes with the second, third and fourth round back.
Pace-setting has been key
The two standout performers of 2021 have undoubtedly got their new year off to a good start and in this tournament that often matters.
Great news for Rahm and Cantlay, but also for Berger and Smith.
No less than 14 of the last 16 eventual winners were tied fifth or better after 18 holes - and 12 of them was tied third or better.
The American made it a trio of time-outers in second because he had packed the clubs in the garage after the Ryder Cup and didn't return until the Hero World Challenge in December.
"My body was telling me to take some time away and I listened to it," he said after bouncing back from a bogey at 17 with an eighth birdie of the day at 18.
"I've played well here in the past, just no necessarily had good results," he added. "A lot of the tee shots suit my eye. I feel like I'm in a good position to win."
Smith made a poor start with a bogey at the second, but then added five birdies and a pair of eagle-3s to best the field.
"Both came from really long putts and quite fortunate really," the Australian admitted. "The course is really receptive, there's no wind forecast this week, so it will probably take something like three more of those to get the job done."
A winner in Hawaii, at Waialae in the 2020 Sony Open, Smith is looking for a first top 15 finish in his third visit to Plantation.
Erik Van Rooyen, Kevin Na and Sungjae Im share fifth after carding 67s, but the chasers below them are not entirely without hope.
History might tell us the leading seven are in a strong position, but the pair who sprung from further back both did so from outside the top 10 - and two winners in the 21st century were outside the top 25 at this stage, albeit their recovery was aided by blustery wind which buffeted the leaders, something Smith knows is unlikely to happen this week.
Among those who will wish otherwise are Viktor Hovland, Bryson DeChambeau, Xander Schauffele and Hideki Matsuyama, who all carded 69s for T13th.
An unlikely paid sharing last place in the field are Patrick Reed and Justin Thomas who needed 74 blows.