Best relishing captaincy showdown with Sexton
They spent the last two months working closely together as two of Ireland's main driving forces, but come Saturday evening that bond will seem like a distant memory as Rory Best and Johnny Sexton look to inspire their respective teams into the last four of the Champions Cup.
Two outstanding leaders in their own right, Best's and Sexton's captaincy styles are at the opposite end of the spectrum.
The Ulster skipper's measured approach rarely sees him come into conflict with referees, while Sexton is never one to hide his emotions in what is a more animated manner.
Romain Poite is the man in the middle for Saturday's sold-out showdown at the Aviva and Sexton will not need to be reminded that he must be mindful of how he speaks to the French official, whose refereeing style can be erratic at the best of times.
Best, on the other hand, should have no such issues as he looks to draw on his years of wearing the armband in such big games.
"We will not be going out to target Johnny," the Ulster skipper insists.
"I won't be having to have that conversation with the ref about protecting Johnny because look, ultimately we will obviously put pressure on him but we will try and put pressure on all of the Leinster team.
"Because if you go after one player in a team like that, there are 14 others who are capable of picking you off.
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"It will be an interesting conversation we have when Poite - at some stage I am sure he will bring us both together to talk during the game. So we will see who can keep their cool in the middle of that.
"Johnny is a fantastic leader within the Ireland squad and he has been doing a great job at Leinster. It will be very strange to be opposite him as opposing captain but he has more than earned the captaincy at Leinster."
Best's and Sexton's leadership qualities came into question from a minority after Ireland's no-show against Wales a fortnight ago.
For the majority of the Six Nations, opposition teams managed to shut Sexton down which invariably meant that Ireland struggled to get into their rhythm. That will not have gone unnoticed up north as Ulster look to upset the odds in Dublin.
"We'll lead in different ways and that will be our challenge within our team," Best maintains.
"With Johnny and the Six Nations, a lot has been made of it, but when you look at our half-backs and the criticism they've received, they've got that because, in their position, they're the best players in the world.
"Look throughout the squad and look at the games they've played well in. They're perceived to have played well in that France game because the forwards got us on the front foot, our set-piece was rock solid, breakdown was good, the outside backs were well organised.
"That's why rugby is so brilliant. because everyone is ultimately inter-dependent on everyone else.
"You need everyone, especially at that top, top level of international rugby. Because they're among the best players in the world and seen as the linchpin of their team, they get the criticism. But the criticism needs to fall on the team and why we didn't function as a team.
"But Johnny Sexton, have no doubt: he is the man for the big occasion. He is still the World Player of the Year. Obviously, you hope, you're not going to see it on Saturday.
"We make a plan to put as much pressure as we can on this Leinster team, him included. You know that he is going to produce something.
"You can try to keep him quiet, but you're not going to keep him quiet for 80 minutes. You know there's something in there that whenever he pulls something (out of the bag) that some of us have to do something magical in defence where you just go, 'wow, how was he able to read that?'
"That's what you're going to have to do against somebody like Johnny."
Ireland went into each of their five Six Nations games with a target on their back and now that Best has returned to Ulster, he knows that the mentality has switched as his side are major underdogs against the defending champions.
"This is the best team in Europe," the hooker adds.
"They have been for a couple of years and definitely last year when you look at what they achieved.
"Teams that beat Leinster are the teams that live with them for 80 minutes and don't have that momentary lapse of concentration.
"It sounds very tough, and it is. That's why they don't lose many games."