Like every contact sport, rugby sometimes demands more than skill, power, pace or a smart gameplan to win. It asks for a body-on-the-line kind of sacrifice from players in the heat of the biggest battles that can't really be taught or practised, but can separate champions from contenders.

Top-ranked Ireland, the best team in the world, faced an acid test of its desire more than its ability at the Rugby World Cup on Saturday against defending champion and three-time winner South Africa.

Ireland came through the expected Springboks barrage in grand fashion in a grit-filled 13-8 victory that might only be a pool-stage win but should silence lagging doubts - if there were any - that the Irish have everything it takes to be world champions for the first time.

“That’s right up there. It was incredibly tough but we fronted up," said Ireland captain Jonathan Sexton, who has played more than 120 tests over 14 years but few as demanding or with as much big-picture meaning as the success over the No. 2-ranked Springboks.

Ireland is the No. 1 team in the world and has been for more than a year. It carried a national record 15-game winning streak into the Springboks match. It has arguably the most varied and tactically astute attack in the sport. Josh van der Flier, the 2022 world player of the year, heads the talent. And there's deep experience in the ranks, starting with the 38-year-old Sexton.

It has also never made it past the quarterfinals at the Rugby World Cup and - in maybe a harsh but fair assessment - has never won a big game at the tournament until now.

“It is huge. It’s wonderful to win," said Ireland coach Andy Farrell. The real value, he said, was the lessons learned for “further down the line.”

The challenge from South Africa, Ireland's closest threat by rankings and a team renowned for taking rugby to the dark corners and making it a dog fight, was: We know you're good enough, but are you tough enough?

Ireland’s answer was an emphatic yes.

“Hats off to Ireland," was South Africa coach Jacques Nienaber's conclusion at the end.

Ireland's precision has been on show in a winning run that's lasted for more than a year, an extremely impressive body of work. But its tenacity and guts were on display more than anything else from the opening minutes to the last against the Springboks in Paris.

Ireland lost its first four lineouts and didn't let that define the game. The Irish scrum creaked at times against a South African pack rated as the best in the world, but never cracked. Sexton felt the force of many South African runners and tacklers targeting him. He came up from one collision in the first half holding his shoulder, grimacing. But he got back to his feet and back in the defensive line, the pain put to one side.

Irish wing James Lowe picked up South Africa's 6-foot-8 behemoth forward Eben Etzebeth in a tackle that turned over possession and underlined everything you needed to know about Ireland's commitment.

In the final moments, Ireland faced up to one last South African forward drive. Irish bodies, exhausted and bruised from 80 minutes of hitting and getting hit, flew in to stop the surge that would have seen South Africa in at the very end and the whole complexion of Ireland's last year change.

The Springboks were stopped.

“Resilience," said Farrell. “That was a proper game that had everything and how we managed to stay on point mentally was fantastic.”

Ireland's mental fortitude was under as much scrutiny as its physical bravery due to that Rugby World Cup record of losing seven quarterfinals in nine tournaments, and not even getting that far in the other two. It might be another intangible element that becomes a factor over the next month in France, when Ireland only faces more stern challenges.

Ireland didn’t finish anything against South Africa. Saturday only set it up to finish top in Pool B and likely face New Zealand, another three-time champion, in the quarters.

But Ireland heads to a final pool game against Scotland and beyond with 16 straight victories and finally knowing and feeling - with all those aching bodies - what it’s like to win a big one at the biggest tournament.

It felt momentous.

“At times we were hanging on in there,” Farrell said, almost relishing how hard it was against South Africa and what coming through it might mean for Ireland this time. "When you love defending as much as we did in that game, that stands us in good stead.”

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AP Rugby World Cup: https://apnews.com/hub/rugby