His opportunity is to tick a box the selectors suspect he's going to have no trouble ticking. Once he does, he'll most likely slip back to the bench for the clash with South Africa as Aaron Cruden is likely to have recovered from his pectoral muscle strain.
Once Daniel Carter recovers from his broken leg this month, Barrett will be competing against the likes of Malakai Fekitoa to lock up that outside back slot on the bench.
So, bottom line, Barrett isn't going to change any pecking order or big-picture thinking with his performance in Napier.
Dagg might, however. But he has to take his game up a level from where it has been in the past 12 months.
The selectors need to see him deliver beyond the table stakes of solid work under the high ball and his raking punt. Competition for places in the back three is such that precision execution of the basic skills isn't enough to guarantee a place.
Julian Savea and Ben Smith do all the basics plus plenty more, which is why they are the two men locked into the mix. Savea provides deadly running and a touch of genius with his handling and decision-making. Smith beats defenders for fun, breaks the line, hauls down escaping Englishmen and pulls off the impossible as an encore.
Those two have set the benchmark high and Dagg, if he wants to earn another run in the fullback jersey, has to rekindle that old magic of his and give the selectors no choice.
There is no shortage of choice in the back three: Cory Jane and Charles Piutau aren't even in the 23 for Napier.
If Dagg wants it to stay that way, he needs to be dancing past people, slicing into the line at astute angles and roaming the backfield before bursting into space from deep.
It's the last skill in particular that needs to be top dollar against Argentina.
When the selectors had to decide after the England series whether to return the previously injured Dagg to fullback, it was his lack of counterattack thrust that put them off.
The opportunity for Dagg is huge - he, rather than Barrett, could be the big winner in Napier.