Southend United 1 Barnsley 3
The Shrimpers started brighter and Mark Gower forced a fine diving save out of Nick Colgan before Nardiello put the Tykes in front.
The ball appeared to have gone out of play before Brian Howard found Nardiello unmarked on the right and he gleefully curled a left-foot shot that beat Darryl Flahavan at his far post.
Blues replied with Steven Hammell floating a free-kick inches over Colgan's bar, before the keeper turned over a Jamal Campbell-Ryce effort.
But the Yorkshire visitors doubled their advantage in the 29th minute when Reid scored straight from a corner on the right.
Colgan then parried a Campbell-Ryce shot before saving Mark Gower's follow-up.
Six minutes into the second half Nardiello grabbed his second when he headed home from close range at the near post from Kyel Reid's right-wing corner.
Southend pulled a goal back on 68 minutes. Substitute Lee Bradbury had been on the pitch four minutes when he headed against the bar.
The ball fell to Adam Barrett whose shot was blocked before a clearance found Gower on the edge of the box.
His right-foot shot cannoned off Colgan's left upright and into the goal.
The goal lifted Southend and they piled on the pressure, while at the other end Barnsley substitute Grant McCann hit the crossbar.
Hammell nearly pulled a second goal back for Blues, but his 25-yard free-kick hit the foot of the post.