Rob Kearney believes Rory Best's Ireland captaincy has been "undervalued".

Ulster stalwart Best has led Ireland to a Six Nations Grand Slam and the nation's maiden two victories over New Zealand in just three years as Test skipper.

Best's stewardship came under intense fire in the wake of Ireland's record 57-15 loss to England at Twickenham on 24 August.

The evergreen 37-year-old hooker impressed off the bench as Ireland edged out Wales 22-17 in Cardiff last weekend though, reasserting his authority, and has since been confirmed as boss Joe Schmidt's World Cup captain.

Now Leinster full-back Kearney has backed Best as the "glue" that can bind Ireland together in their bid to push past the World Cup's quarter-finals for the first time in the Japanese tournament that kicks off later this month.

Asked to evaluate Best's leadership, Kearney replied: "It's huge, isn't it? And sometimes I think it gets a bit undervalued, his win rate and what he has achieved.

"Some of the momentous victories we've had as a team have been under Rory. He's a brilliant leader, he's the glue that brings the team together a lot.

"Again, he's a guy who is training really well and I'm sure he's very excited to get out there and demonstrate that he's still hugely capable of producing big performances, even at his ripe old age."

Best will retire after the World Cup in Japan and will make his final Ireland turn at the Aviva Stadium in winning his 120th cap in Saturday's clash with Wales.

Ireland's last World Cup warm-up fixture also represents head coach Schmidt's final Test at the helm in Dublin, with the 53-year-old Kiwi stepping down after the World Cup.

Kearney admitted Ireland would love to hand both men the perfect Dublin send-off, but insisted that cannot cloud preparations.

Ireland will launch their World Cup by facing Scotland in Yokohama on 22 September, with Kearney hoping Schmidt's men can take another leap forward in form this weekend.

Asked how keen the Ireland squad are to help Best and Schmidt sign off in style in Dublin, Kearney said: "Obviously it's very important but it's not at the forefront of our minds.

"Performance is huge for us this week and even if you scale back the performance, it's putting it into blocks; the first 10 minutes, the second 10 minutes, and so on.

"If we can look after all those mini blocks and win all those moments, the performance and victory will look after itself. And then you get to enjoy and feel proud of giving Joe and Rory the big send-off.

"Facing Scotland in round one in Japan, it's a different make-up from how the pool games fell for us four years ago. We really need to ensure we're firing at all cylinders for that first week, so this weekend is a big step for us.

"That's the biggest game of the pool probably for us. And we know that Scotland are starting to brim nicely, they got a good win over France at home. So facing Wales at home this weekend, it's also a perfect Test for us; it's as tough as it gets.

"The guys last week made a big step in terms of the team's confidence. To get a win on the board away from home was big for us.

"We've trained really well this week which will give us another lift in confidence. But performance-wise now we need to take another big step." 

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