Behind Rahm and Smalley there was a three-way tie on five under between American two-time champion Justin Thomas, Sweden’s Ludvig Aberg and little-known German Matthias Schmid.
Former world number one Thomas had posted the early target after a five-under 65, then sat back in the clubhouse to watch and wait patiently, while hoping for a “little bit of help” to win.
The wind did not whip up as Thomas hoped. Yet, with the severely sloped greens playing firm in the Pennsylvanian sun and the thick rough continuing to be penal, scoring opportunities remained at a premium.
For almost everyone other than Rai.
All week long it felt like a strategic thinker would be the one to prevail, and Rai, known on tour for his diligence, carefully plotted his way to victory.
Keeping his ball on the fairway from the tee proved to be an effective tactic – he was joint second best on Sunday and fourth for the week – which others did not find as simple.
Once Rai moved clear of the pack on seven under – thanks to birdies on the 11th and 13th – it looked like a score which would not be caught.
In what was now by far the biggest moment of his career, an emotionless Rai stayed in the zone. The experience of beating a strong field at the DP World Tour’s Abu Dhabi Championship in November was perhaps something he was able to draw on.
Another tap-in birdie on the par-five 16th put more daylight between him and the pack, before a putt from the other end of the measuring stick put victory within touching distance.
Rai somehow negotiated an impossible-looking putt to move three shots clear of his rivals. Only then did he show a flicker of emotion.
But the gentle fist pump as the fans around him went wild was telling and perfectly encapsulated how Rai has become a major champion – by keeping calm in the eye of the storm.
“I definitely wasn’t trying to hole that putt,” Rai smiled as he clutched the Wanamaker Trophy.
“The shadow of the pin gave a really nice line for the last 10 feet so that helped with the visual.
“It just tracked really well – it was amazing to see it go in.”
Rai is only the eighth Englishman to win a major since World War Two, joining Henry Cotton, Max Faulkner, Tony Jacklin, Nick Faldo, Justin Rose, Danny Willett and Matt Fitzpatrick.
It also means UK golfers have won the first two of the year’s four annual majors for the first time, after Rory McIlroy defended his Masters title in April.