Roberts will be a handful, Drico warns

The Lions' midfield partnership of 2009 will cross swords in Saturday's potentially thrilling World Cup quarter-final at Wellington Regional Stadium.

Roberts has been in explosive form in New Zealand and O'Driscoll insists he has become a more formidable opponent since adding variety to his game.

"Most of the Welsh squad are in good form. Jamie Roberts has done well, mixing his game up well. He'll be a handful, but that's nothing new," he said.

"Jamie carries extremely hard, but he's also brought in some nice subtleties.

"He's not afraid to mix it up and that's made him difficult to read.

"He's evolved on that front, but one aspect of his game that hasn't changed is his ability to break the gainline.

"Teams play off go-forward ball and he's one of their go-to guys for that."

Ireland enter Saturday's showdown as marginal favourites to reach the semi-finals for the first time.

One of the key ingredients behind their unbeaten march through the World Cup has been their rampaging back row of Sean O'Brien, Stephen Ferris and Jamie Heaslip.

O'Brien and Ferris have been wrecking balls while the industry of Heaslip, the only member of the squad to have played every minute of the tournament, has enabled them to flourish.

The trio have been touted as the best back row in the tournament -- New Zealand, Wales and South Africa are pushing them close.

"They've been going very well," O'Driscoll said.

"On their day they're a world-class trio."