THERE ARE COMPLEXITIES to rugby which can make it inaccessible to the uninitiated but, when the game is in full flight, there is equally a simplicity to it: 15 players trying to run through, or around, 15 other players.

For about an hour of Leinster’s 20-17 Champions Cup semi-final victory over Northampton at Croke Park, the Saints were broadly unable to do that as Leinster’s blitz defence held them underwater. But in the final quarter, Northampton’s vaunted attack finally surfaced and the Premiership leaders almost pulled off a miracle which would have rivalled Leinster’s similar turnaround in the 2011 final between the same clubs.

Leinster captain Caelan Doris combined with replacement Jack Conan for the decisive intervention, thwarting Saints’ comeback attempt with a jackal penalty. At full-time, Doris’ face told the story of the game as he turned to the same player with a smile and breathed out an expletive of pure relief.

“We came together and acknowledged that there was a bit of a lull, that they were going through a bit of a purple patch,” Doris said of the second half.

“Some of that was through our discipline, giving away back-to-back penalties which gave them entry into our half, but I think it’s credit to them as well. They’re top of the Premiership for a reason.

When we were scouting them, we saw their attack as one of the best we’re going to face this season and you saw some of that in the second half as well. As much as we back our ‘D’, their attack probably got on top of us at times there.

“It was just pleasing to just about do enough in the last few minutes.”

Pre-game, Northampton fullback George Furbank had openly admitted that his side had been working on stopping scrum-half Jamison Gibson-Park, whom Saints had identified as the man who “runs the show” for Ireland’s eastern province.

Saturday was a day on which Phil Dowson’s excellent, up-and-coming side learned several harsh lessons — and one of them was you’re probably better off planning around Gibson-Park than planning specifically for him. The 32-year-old has become that good.

Post-match, the New Zealand-born nine played down his ascent in recent years as being merely a byproduct of working in an elite environment.

Encouraged further to provide some of the thinking behind his quick tap and rasping skip pass which yielded Leinster’s first try for hat-trick hero James Lowe, Gibson-Park replied: “It’s probably intuitive to a point.

“A lot of players… Not to talk myself up, but they’ve all played with me long enough now to know I’m going to be looking for those sort of opportunities.

“So, Lowey certainly is somebody who is on the same wavelength. It’s not really a call, but you see it as well.”

As for his second assist for Lowe, a volleyball-style palmed pass out to the unmarked left winger after the ball had been half-ripped from Doris on Saints’ line, Gibson-Park joked with the man beside him: “I dunno, I was hoping Caelan was going to pass it to me earlier.

“I don’t know, it came and popped up to me and them’s the breaks sometimes. I was lucky enough it came off.”

And that’s enough talking about himself.

Doris, too, was quick to share credit with Jack Conan for the dig-out with the match-winning turnover, and Leinster’s captain had a similar explanation for his read on that penultimate breakdown and why he decided to risk the poach with Northampton only three points down and in kicking range.

“It’s more instinct, you don’t really have time to weigh it up too much,” the Ballina man said.

“The context of the game, it felt like we needed a moment like that but you don’t want to go overly hunting for them. If it shows up…

“I was actually on the outside and that’s against our ‘D’ system, coming in like that, but I’d the security of Jack on the inside.”

In what was Leinster’s first appearance at Croke Park in a rugby generation, the Ireland back row described the atmosphere as being “a level up”, and more affecting than the Aviva Stadium.

“From doing the lap at the start of the warm-up”, Doris said, “and when we got around to Hill 16 especially, you could feel the energy and the noise from the crowd. It was special.

When we ran out for the first half it was a step up from what we’ve experienced in the Aviva, probably because of the nature of it being a rare occasion to play here.

“So many fans travelling over from the southside, I’m sure we’d a few from the northside as well and from the rest of the province, but it was a great atmosphere.”