Agnew double downs the Hammers.
Agnew gave the young Black Cats the lead before Taylor Tombides levelled for the visitors on the stroke of half-time.
Agnew won it for the hosts from the penalty spot after James Stinson was brought down in the area.
Peter Burke was busy throughout in the Sunderland goal, pulling off a fine save after just two minutes as Tombides looked certain to score from six yards.
The deadlock was broken on 11 minutes as Ross Holland played in Agnew on the right side of the area and the midfielder smashed into the top corner leaving Sam Howes in the Hammers goal with no chance.
Ross Holland then went close for Sunderland, forcing a fine save from Howes as Holland’s left shot look destined for the top corner.
West Ham levelled on the stroke of half-time Lewis Page headed back across goal for Tombides to finish from eight yards.
The Black Cats were again thankful to their keeper, Burke, as he again saved from Tombides in a one-on-one situation at the start of the second period.
And, that save proved to be valuable as Agnew grabbed the eventual winner on the hour mark. Stinson was pulled down, as he looked to score himself, and Agnew stepped up and coolly rolled the ball into Howes’ bottom right hand corner.
The Hammers through bodies forward in the closing stages but Sunderland showed resilience to grab a valuable three points in the Barclays U18 Premier League.
Sunderland: Burke, Lane, T Robson, Ledger, Beadling, Sukar, Noble, Agnew ©, Stinson, Holland, Smith.
Subs not used: McCarthy, Purvis, Blinco, McGrath