Ireland's replacements bench heavy artillery will be useless unless the starting line-out subdue potent Samoa, warns assistant coach Les Kiss.
Brian O'Driscoll sat out part of Ireland's team run at the Aviva Stadium in their final session before Saturday's opening autumn international against Samoa.
Specialist defensive coach Kiss confirmed O'Driscoll is fully fit to start though, and only sat out as part of a workload agreed with head coach Joe Schmidt.
Cian Healy, new full-time captain Paul O'Connell and muscular flanker Sean O'Brien all lie in wait on Ireland's bench to be unleashed in the second half against the Pacific Islands nation.
Experienced 50-cap scrum-half Eoin Reddan and accomplished Leinster out-half Ian Madigan are also named among the replacements.
New boss Schmidt is renowned for stacking his benches to unleash a bevy of second-half talent and change the complexion of a match if required.
Kiss admitted the new Ireland chief will transfer that Leinster tactic to the national job - but said those assets will be useless without big impact from the starting XV.
He explained: "You can look at that bench and say there's a fair bit of strike power there. But that's for later in the game.
"We've got to make sure we start the game well and put ourselves in a strong position.
"If we don't do that then the bench won't be important and won't be able to make any impact at all.
"They are a lethal unit if they get going, so we've been making sure our guys have their heads in the right place for this game.
"When you haven't got the ball against this team, the minute you switch off or decide to take a rest, you'll be found out in one aspect or another.
"They've got some big powerful forwards who can go through the middle, or work around the edges of the ruck.
"Tusi Pisi is a real handful at fly-half if you give him space to work, and Johnny Leota and Pisi have built a great combination in midfield there.
"Their running lines and the way they can carry and damage a defensive line are things we need to be aware of, and they have a lot of speed.
"But they don't mind kicking the ball either, in varying situations, to challenge your back field.
"It really is a challenge across the park, so defensively we've got to have our hats on.
"They can hurt you at any time, and it really is a challenge against this side.
"I think in the last five Tests they have averaged three tries a Test, and that's against good teams, beating Wales amongst that, beating Scotland and Italy.
"So they will be very confident about where they are."