Everything was shocking about Kevin O'Brien's World Cup hundred against England. His hair, his shots, the win. And that it was Kevin O'Brien.

I mean Kevin O'Brien. Not his brother Niall, not Trent Johnston, not William Porterfield or Ed Joyce. At one stage O'Brien complimented Jimmy Anderson on a good ball, Anderson asked how O'Brien would know what a good delivery was and O'Brien retorted that he knew what a bad one was, and he'd just smashed one of them away for six. Sledging Jimmy, heaving 113 from 63, breaking world records, six sixes and Ireland beat England. The whole thing was crazy. O'Brien was rated by no one outside Ireland and was slapping balls around everywhere like, well, as no one had ever before in a World Cup.

It was that day, as much as any, that changed Ireland's history. And if not that day, it was the 2007 World Cup win over Pakistan, in which O'Brien was second top score behind older brother Niall and remained unbeaten when Johnston hit the winning runs. The three most significant games in Ireland's history, Kevin O'Brien has been there. For Ireland, O'Brien is always there.

Outside Irish cricket, O'Brien has never had much impact on cricket. A few T20 franchise contracts, some List A in England, but even then he rarely grabbed attention.

Then he plays for Ireland. Some players play much better for their country than they do for their clubs. You see, the plodding power forward from the NBA who suddenly at the Olympics is some brutish enforcer, or the journeyman pro tennis player living the good life until he fires up for the Davis Cup. That is not quite the case for O'Brien; his numbers suggest he's been as good for everyone else as he has been for Ireland. The real difference is when O'Brien is astonishing, it is for Ireland.

In the first innings, his top order was smashed in the face by Pakistan bowlers. They were playing for lunch like it was the last meal. Gary Wilson was off getting his arm fixed, and it was O'Brien who had to come in before there were ten runs on the board. His innings started as nervously as anyone, but he soon took control, and he looked like he belonged.

The man who has only played two first-class games in county cricket - one for Surrey, one for Notts - and just 41 first-class games overall dating back to his 2007 debut in the Intercontinental Cup against the UAE, seemed like the Test match player Ireland needed. And then after scoring more than half of Ireland's runs up to that point, he got caught in the ring. He was filthy, shaking his head, mumbling at himself and kicking at the ground. He felt like he'd let his team down when actually he was the first to stand up.

But he always stands up. While other players have been better than O'Brien, no one's been more representative of Irish cricket. England would never come calling and take him away. He has 300 caps, more than any Irish player. He's almost always available. While some Associate nations in their moments of success have been accused of being a team of ex-pats, Ireland had O'Brien: an Irish underage cricketer, with an Irish playing brother, and father, plus a flock of ginger hair. In O'Brien, Ireland had a poster child for Irish cricket. He's their giant ginger mascot who hits sixes and wins games.

Today he didn't hit sixes. His 50 came up off 100 balls, completely inverse to his 100 off 50 against England. We've had O'Brien the bludgeoner; today we had O'Brien the nurdler. He poked and prodded, ESPNcricinfo's stats say the flick was his most successful shot, most of the time he knocked the ball towards cover point for a single. There was a french cut, a bunch of composed leg glances. Edges past slip, short of slip, balls ending up near the stumps. It wasn't always regal, but it was stoic.

If Irish cricket had a player type they're known for, it would be allrounders who aren't quite top level bowlers but often compensate with the bat: Stuart Thompson, Trent Johnston, John Mooney and Alex Cusack. For Irish cricket, there is nothing special about what O'Brien does, but there is everything special about when he does it.

And that doesn't even mention Pakistan, who seemed to stop playing at one point, putting fielders out when they were still well on top, and Ireland was making the odd mistake. Maybe their best error was when O'Brien - on 91 - swept a ball to short fine leg, who missed, only for the deep backward square to come around to mop up, which he did not. Pakistan made errors, O'Brien did not.

Against England, in that World Cup innings, he was playing brutish slog sweeps of raw, ungainly violence. Here he was at the non-striker's end in Malahide after another eased single, practising his lap sweeps. He looked like an ogre trying to play with a children's tea set. Getting O'Brien to draw this match was like asking a steamroller to solve a moral philosophy question.

But he worked on it. He wasn't massively in control but it was a chanceless hundred, albeit with one close lbw shout against Rahat Ali on 69 the only tight call. The ball wasn't hitting the middle of his bat but he fought hard. He fought Pakistan's bowlers, the match situation and his own instincts. Because O'Brien doesn't really play many first-class innings, he is almost never the anchor, and he's paid for fireworks not defence.

In a career spanning more than a decade, he has made only one first-class hundred, an unbeaten 171 in a first innings run-fest against Kenya - his brother Niall and Andre Botha also made centuries in Ireland's 578 for 4 declared - at Nairobi that set up an innings win in the Intercontinental Cup in 2008. His last hundred for Ireland was that World Cup innings against England, seven years ago.

Today he played like a man who doesn't make many hundreds. Around 80 he played and missed at a ball and then violently swung his bat over the stumps before being calmed down by Stuart Thompson. Then when he got to the 90s, the pressure got to him.

On 97, there was a glimmer of his hundred before the ball that went to the fine leg boundary was signaled four leg byes, or as O'Brien said to Tyrone Kane, "Bloody leg byes". Then there was a nervy steer along the ground near slip before he did some quadriceps yoga poses at the non-striker's end because, "I'm getting old and I'm not used to batting for five hours".

On 98, he failed to get a ball away, which frustrated him so much he missed the next delivery, in which Shadab Khan appealed for a caught behind. Pakistan then brought on Mohammad Amir, who had been incredible earlier in the day. On 99, he went about as close to edging the ball behind as he could, before a leading edge popped up on the offside and fell safely through point to ensure that O'Brien made his second first-class hundred.

"It's nice to be on the imaginary honours board in these Portakabin changerooms". There was no massive celebration, he didn't even rate it as is his best innings. He said, "I'm just old, man. Batting for five hours takes its toll. I'm not used to playing these longer form games". And as always he's looking forward to the next day, the next job for Ireland. Because that's what O'Brien lives for.

If Irish cricket had a player type they're known for, it would be allrounders who aren't quite top level bowlers but often compensate with the bat. Stuart Thompson, who allowed O'Brien to make this innings, is one. Trent Johnston, John Mooney and Alex Cusack are just a few others. For Irish cricket, there is nothing special about what O'Brien does, but there is everything special about when he does it.

There are - and will continue to be - better Irish players than O'Brien. He's not the best player in this team, he's possibly not the best player in his family. But because of when he stands up, you wonder if there will ever be another player who will play three innings as vital as he has for his country.

It was shocking that O'Brien scored a hundred, that Ireland lasted a whole day, and that Ireland could win this match. But this time, it wasn't shocking that it was Kevin O'Brien. It's always Kevin O'Brien.

Kevin O'Brien, Test centurion.

Jarrod Kimber is a writer for ESPNcricinfo. @ajarrodkimber