Preview: Ireland v Wales
Ireland have won the last two Six Nations and if they want to be victorious for the third consecutive time – something no team has managed since Italy joined the tournament – then Sunday's match in Dublin could be key.
O'Brien is well aware of his counterparts in Wales' back row, having toured with Taulupe Faletau, Dan Lydiate, Justin Tipuric and Sam Warburton with the British and Irish Lions, and the Welsh line-up will include impressive power throughout.
"The first thing they bring is that huge physicality," O'Brien told the Irish Times.
"They have a good kicking game, they're good in the air, they've a big pack and they've a great back row. They've a lot of strings to their bow.
"The physicality one is one which they pride themselves on. It sets the tone for them."
This year will be the first Six Nations since 1999 where Ireland have been unable to call upon the services of either Paul O'Connell or Brian O'Driscoll.
It means 2016 will see a new Ireland captain lead the side out in the shape of hooker Rory Best and O'Brien is ready to help lead the troops – something he has tried to do for some time.
He added: "I want to be a leader within this environment. That means I have to have all my ducks in a row and make sure I'm performing as best as I can and letting the other people around me see that.
"[But] nothing really changes for me in terms of what I want to do on the field."
Sam Warburton has urged his teammates to kick off their 2016 Six Nations campaign with a bang, as the Wales captain looks to avoid a repeat of their 2014 nightmare.
Two years ago Warburton was part of the Wales side that were beaten 26-3 by Ireland in Dublin.
After avoiding a trip to Ireland in last year's Six Nations, the Aviva Stadium is the scene for Wales' opener in this year's Championship.
And Warburton, who will be in the No.6 jersey on Sunday, knows just how important it will be for Wales to silence the Aviva Stadium crowd as early as possible.
"They just got a really good start. We had to defend quite a few phases for the first 20 or 30 minutes," said Warburton.
"All I remember is the Irish crowd were so loud and you could see the team feeding off that, and they kept growing through the game.
"Trying to stop that early on will be pretty important. You want to start every international game well, but in particular on that occasion I can remember them getting their tails up as soon as the crowd started getting behind them.
Players to watch:
For Ireland: Now doubt that new captain Rory Best, taking over from the legendary Paul O'Connell, will have a substantial portion of the spotlight on him. And at lock Devin Toner will be looking to fill the void left by O'Connell's departure in the second row. Another player that will be closely watched is star flyhalf Jonathan Sexton – not just because of his obvious talents, but to see if he has truly recovered from the latest bout of concussion. And then there is South African CJ Stander, on debut for his adopted country.
For Wales: It starts with the New Zealand import at fullback, Gareth Anscombe, followed with star backs like George North, Jonathan Davies, Jamie Roberts, Dan Biggar and Gareth Davies. However, it is up front where Wales may just have the biggest advantage – a loose trio of Taulupe Faletau, Justin Tipuric and Sam Warburton (as captain), to go with the world class second row of Alun Wyn Jones and Luke Charteris.
Head to head: At the time of writing the Ireland starting XV had not yet been confirmed, but you could look forward to two very exciting fullbacks in Simon Zebo (Ireland) and Gareth Anscombe (Wales). In the midfield there is Jared Payne, Robbie Henshaw for Ireland, against seasoned Welsh veterans Jonathan Davies and Jamie Roberts. However, the most interesting battles will be up front – starting with the second row where Ireland will field a new combination in Devin Toner and Mike McCarthy against the established world-class Welsh duo of Alun Wyn Jones and Luke Charteris.
Recent results:
2015: Wales won 16-10, Dublin
2015: Ireland won 35-21, Cardiff
2015: Wales won 23-16, Cardiff
2014: Ireland won 26-3, Dublin
2013: Ireland won 30-22, Cardiff
2012: Wales won 23-21, Dublin
2011: Wales won 22-10, Wellington (World Cup quarterfinal)
2011: Wales won 19-13, Cardiff
2010: Ireland won 27-12, Dublin
2009: Ireland won 17-15, Cardiff
Prediction: The bookmakers are favouring Ireland, as they often do with the home team, but a large majority of the punters have put their money on Wales. It may well be because Wales have a far more settled look about them than an Irish team that is without two of their biggest legends – Brian O'Driscoll and Paul O'Connell. Wales may well steal this, but it will be in the single digits and may well come done to one kick or one try.
Teams:
Ireland: 15 Simon Zebo, 14 Andrew Trimble, 13 Jared Payne, 12 Robbie Henshaw, 11 Keith Earls, 10 Jonathan Sexton, 9 Conor Murray, 8 Jamie Heaslip, 7 Tommy O'Donnell, 6 CJ Stander, 5 Devin Toner, 4 Mike McCarthy, 3 Nathan White, 2 Rory Best (captain), 1 Jack McGrath.
Replacements: 16 Sean Cronin, 17 Jerry Cronin, 18 Tadhg Furlong, 19 Donnacha Ryan, 20 Rhys Ruddock, 21 Kieran Marmion, 22 Ian Madigan, 23 Dave Kearney.
Date: Sunday, February 7
Venue: Aviva Stadium, Dublin
Kick-off: 15.00 (15.00 GMT)
Expected weather: The rain that starts on Friday will continue through to Saturday and the wind will pick up to about 40 kilometres per hour. It will be a high of 8°C and a low of 3°C, but the wind chill factor will push it down to -1°C by kick-off.
Referee: Jérôme Garcès (France)
Assistant referees: Glen Jackson (New Zealand), Ben O'Keeffe (New Zealand)
TMO: Graham Hughes (England)
Sources: @rbs_6_nations & @rugby365com
