All seven replacements in last weekends historic 17-12 defeat of South Africa at Lansdowne Road have earned a recall to coach Eddie OSullivans starting line-up and Humphreys, 33, is one of many with a point to prove.

Munsters Frankie Sheahan - without a start in two years - Marcus Horan and Donncha OCallaghan, Leinster duo Guy Easterby and Eric Miller and 65-cap veteran Kevin Maggs, now of Ulster, all earn rare starts along with Humphreys, with OSullivan insisting: The team for Argentina isnt picked yet.

There are guys who are coming into the team now who are chomping at the bit. Maybe they havent had a lot of Test rugby or have been coming off the bench.

Ireland face Argentina in Dublin on Saturday week - coincidentally the same opposition as when Humphreys last started for Ireland during last years World Cup.

OSullivan added: These fellas have a point to prove - South Africa is done and dusted, it was a great performance but its yesterdays news now. We raised our standards against the Springboks and the trick now is to maintain them. Thats the benchmark.

Humphreys, who will break through the 500-point barrier against the Americans with a nine-point haul, said: Weve got to get the focus right on the day. The US may be classed as weaker opposition, but well treat them with the respect they deserve.

Every international game could be my last one, so thats the way I look at it. Ill enjoy it by playing well and winning. My first priority is always to go out, play well and enjoy it, and try to bring the best out of the younger players who have a huge opportunity on Saturday.

Both Humphreys Ulster colleague Tommy Bowe and Munster flanker Denis Leamy will make their senior debuts against the 16th-ranked Eagles.

USA coach Tom Billups has made four changes, one positional, to the side that lost 39-31 to France in Connecticut in July.

Lock Alec Parker, blindside flanker Brian Surgener and right wing Al Lakomskis return, with captain Kort Schubert of the Cardiff shifting to number eight.

We have to get a lot of things right on the day, admitted former Eagles captain Billups.

Were looking for a good performance and a smart one in the conditions.

Ireland: G Murphy; S Horgan, B ODriscoll, K Maggs, T Bowe; D Humphreys, G Easterby; M Horan, F Sheahan, J Hayes, D OCallaghan, P OConnell, S Easterby, D Leamy, E Miller.

Replacements: S Byrne, S Best, L Cullen, A Foley, P Stringer, R OGara, G Dempsey.

USA: F Viljoen; A Lakomskis, P Emerick, S Sika, D Fee, M Hercus, M Timoteo, M McDonald, M Wyatt, J Waasdorp, A Parker, G Klerck, B Surgener, T Petruzzella, K Schubert(captain).

Replacements: M Hobson, C Osentowski, J Gouws, F Mounga, D Williams, M Sherman, A Tuipulotu.