Sunderland suffered their first away defeat of the season when they sank without trace at 20th-placed Barnsley.
Simon Grayson's side, roared on by a passionate 4,000-plus-strong away following, produced some bright attacking play early on, only to be stung by two first-half goals inside five minutes.
On-loan Chelsea and England Under-20s striker Ike Ugbo put the Yorkshire side ahead with Harvey Barnes doubling the lead.
Just before the mid-point in the second half, George Moncur sealed the deal with a shot into Robbin Ruiter's top-right corner.
Grayson had made two changes, preferring Ruiter between the sticks, following an impressive showing at Carlisle, while Bryan Oviedo made his first start.
Sunderland had enjoyed so much of the play in the first half hour only to be shattered by two goals inside five minutes.
Hammill did some good work in the build-up before Barnes put in a low cross from the left which UGBO bundled in from inside the six-yard box.
Sunderland had barely recovered from that when they conceded a second in the 35th minute.
Hammill was again involved, crossing from the right with Ty Browning's weak header falling invitingly for BARNES who lashed his volley high into the net.
Sunderland were were left frustrated and furious five minutes from the break when Lee Cattermole sent James Vaughan clear only for Liam Lindsay to bring him down.
Not only did Chris Kavanagh NOT award a spot kick, he only showed the home defender yellow card.
And to add insuly to injury, Aiden McGeady put his free-kick wide of the target.
There were appeals for a second-half penalty when Vaughan went down under pressure from Lindsay and Matty Pearson from McGeady's cross but Mr Kavanagh would have none of it.
And there were more claims soon after when Grabban crumpled to the turf, too easily it has to be said, under Jackson's challenge.
There had already been a blast of "Are you watching Elllis Short?" before the away support were sent into a rage by a third Barnsley goal.
When Ugbo sent MONCUR down the left, there looked little danger only for the attacking midfielder to let fly with a left-foot shot Ruiter should not have been conceding at his near post.
Grayson introuduced both Lynden Gooch and Wahbi Khazri though to no avail.
Barnsley: Davis, McCarthy, Jackson, Lindsay, Pearson, Williams, Potts, Moncur, Hammil (Thiam 90), Ugbo (Bradshaw 71), Barnes (Hedges 66).
Unused Subs: Townsend, Pinnock, Mowatt, Bird
Goals: Ugbo 31, Barnes 35, Moncur 65
Booked: Lindsay 40
Sunderland: Ruiter, Jones, Kone, Browning, Oviedo (Matthews 81), Cattermole, Ndong, McGeady, Honeyman (Khazri 65), Vaughan (Gooch 55), Grabban
Unused Subs: Steele, O'Shea, Gibson, Asoro
Boooked: Oviedo 77, McGeady 86, Khazri 90
Referee: Chris Kavanagh
Attendance: 15,697 (Away 4,249)