SLOPPY first-half defending sentenced Albion to a second defeat inside three days at bogey ground Oakwell.
The Baggies haven't won at the South Yorkshire stadium for 62 years.
And they never looked like bucking that trend when Adam Hammill was allowed to force home the opener on 14, before Iain Hume made it 2-0 from the penalty spot just past the half-hour mark.
Albion improved after the break and camped themselves in the Tykes half - but they just could not breach the hosts' stubborn resistance.
And the Baggies' misery was complete ten minutes from time when Shelton Martis put through his own net.
Chris Brunt bagged a late consolation with a 30-yard cracker two minutes from time.
Chris Wood was handed his first start in eight games in place of knee-injury victim Luke Moore while fit-again Brunt replaced Gonzalo Jara, who dropped to the bench.
Barnsley's three changes saw call-ups for Baggies legend Darren Moore, new loan signing from Southampton, keeper Bartosz Bialkowski, and Jon Macken. David Preece, Andy Gray and Jacob Butterfield made way.
Albion started the game knowing a win against third-bottom Barnsley would propel them back to the top, with pre-match leaders Newcastle not facing QPR until tomorrow.
The hosts recorded the first effort on goal in the third minute, with Hammill failing to trouble Scott Carson with a 25-yard drive.
But Albion gave the Tykes defence real cause for concern moments later with a flowing move which resulted in Roman Bednar controlling Youssouf Mulumbu's lay-off and firing at Bialkowski from 15 yards.
It was the Baggies rearguard who were back-tracking in the seventh minute and the unmarked Macken was inches away from poking home at the far post following a terrific right-wing run and centre from Anderson De Silva.
Barnsley defender Carl Dickinson was fortunate to stay on the field in the 11th minute when he scythed Bednar down with what looked like a knee-high challenge on the edge of the Barnsley box.
Fortunately for Albion, Bednar was able to continue after lengthy treatment.
But Albion shot themselves in the foot on 14 when they conceded the softest of goals.
The visitors made a real hash of dealing with a Macken centre and Hammill was allowed to swivel before giving Carson no chance from close range.
Albion had another scare five minutes later when Hume controlled Macken's flick-on and squeezed between centre-halves Jonas Olsson and Martis before firing straight at Carson from 15 yards.
The Baggies were still very much trying to find their way as the half passed its midpoint as they continued to look wobbly at the back while too many passes were going astray.
And it was Barnsley who threatened again on 27 when Carson was well positioned to catch Hammill's 25-yard pile-driver.
But the Tykes almost handed Albion a lifeline a minute later when Dickinson miscued a clearance high into his own box. Under pressure from Wood, Bialkowski dropped the ball but there was no-one on hand to poke the loose ball home and Barnsley cleared.
Albion then carved out their first real chance when Robert Koren raced onto a huge Carson punt upfield before crossing to Bednar. The Czech striker looked certain to score but failed to make any contact with only Bialkowski to beat and the danger was cleared.
The Baggies had a mountain to climb in the 31st minute when they conceded a penalty after a push by Zuiverloon on Macken.
Hume made no mistake from 12 yards, sending Carson the wrong way to double Barnsley's lead.
Incredibly, it almost got worse for the Baggies in the 35th minute when the unmarked Macken fired over from 15 yards from Hammill's centre.
Albion managed to regain some composure as the half drew to a close and Olsson had his head in his hands when he directed a free header wide from Dorrans' corner.
But back came Barnsley and after Hammill had left Zuiverloon on his backside and centred, Mulumbu and Olsson combined to scramble Macken's close-range stab wide.
Albion registered their best effort of the half three minutes into stoppage time.
Wood flicked Martis' diagonal ball into Dorrans' path and only a wonderful finger-tip save from Bialkowski kept out the Scotland Under-21 international's vicious 18-yard volley.
Di Matteo rang one change during the interval, replacing like for like as injured central midfielder Mulumbu made way for Jara.
And the Chile international made an instant impact as Albion started brightly.
Jara found Bednar on the edge of the Barnsley box and the Baggies No.9 drew a fine save out of Bialkowski with a stinging drive.
Albion continued to pile forward but Dorrans could not get any real purchase on a decent shooting chance from Wood's lay-off.
Barnsley were inviting Albion on by sitting deep in their own half, but too many long balls were easily mopped up by Messrs Moore and Co in the Tykes rearguard.
Albion made a further change on 61, with Simon Cox replacing Wood, who had really been through the wars.
Cox was straight in the thick of it, showing one or two nice touches before flashing a header inches wide from Zuiverloon's terrific centre.
Brunt was the next to go close when he fizzed a 30-yard free-kick just wide of the far post.
Barnsley did not really threaten again until the 69th minute when Joe Mattock was forced into a frantic goalline clearance as Ryan Shotton tried to force home Hume's corner.
Moments later, Macken was allowed to turn and shoot from 18 yards, but the ball flew straight at Carson.
Albion surged straight upfield and only Shotton's point-blank block prevented Bednar's far-post header finding the net from Zuiverloon's cross.
From Dorrans' ensuing corner, Martis towered above the Barnsley defence but could only head over.
It was all Albion now but the goal just would not come.
And it was all over ten minutes from time.
Barnsley sprung forward after Albion gifted them possession and Martis inadvertently stabbed the ball into his own net from Hammill's centre.
Brunt restored some pride by smashing home a stunning 30-yard drive, which completely wrong-footed Bialkowski, to register his third goal in just two games.
But that was all the Baggies had to show for their efforts following yet another night of woe at Barnsley.
BARNSLEY (4-4-2): Bialkowski; Shotton, Foster, Moore, Dickinson; De Silva (J Gray 45), Doyle, Colace, Hammill; Macken, Hume (Campbell-Ryce 76). Subs not used: Rusling (gk), A Gray, Kozluk, Bogdanovic, Butterfield.
ALBION (4-4-2): Carson; Zuiverloon, Martis, Olsson, Mattock; Brunt, Mulumbu (Jara HT), Dorrans, Koren (Reid 82); Wood (Cox 61), Bednar. Subs not used: Kiely (gk), Barnett, Meite, Teixeira.
GOALS: BARNSLEY - Hammill (14), Hume (pen 31), Martis (own goal 80). ALBION - Brunt (88).
BOOKINGS: BARNSLEY - Dickinson (foul 11). ALBION - Mattock (foul 82).
REFEREE: S Mathieson (Cheshire).
ALBION STARMAN: Chris Brunt.