A disappointing first half performance saw Orient slip to their sixth consecutive away defeat and move deeper into the relegation zone.
Strikes from Conor Hourihane and Kane Hemmings were enough to kill the game before the interval and despite seeing more of the play and playing against 10 men for the last 15 minutes, Orient failed to find a way back into it.
Fabio Liverani made two changes as he went in search of his first win in charge of the O’s. Dean Cox dropped to the bench as Gianvito Plasmati returned to partner Shaun Batt in attack. At the back Nathan Clarke missed out with a hamstring strain, meaning Elliot Omozusi came in at right back with Scott Cuthbert taking over the armband and a spot in the heart of the defence.
It was a quiet start from both sides as the cold wind swept in to Oakwell. Batt scored his first goal in over a year last weekend and looked in the mood for another as he spun and shot wide after six minutes from the edge of the box.
The chance seemed to wake Barnsley from their slumber as two minutes later Kane Hemmings really should have broken the deadlock but could only volley wide after good work from Dale Jennings.
They would not have to wait long for their goal though as Hemmings cut the Orient defence in half with a perfectly weighted through ball for Conor Hourihane to round the goalkeeper Adam Legzdins and slot home.
Things got worse for the O’s two minutes later when Plasmati who had already pulled up with a hamstring problem, finally made way for David Mooney.
The switch seemed to aid the O’s as Mooney dropped deep to pick up the ball and link the play, though despite seeing more of possession, Ross Turnbull remained a spectator in the Tykes’ goal.
As the half wore on Barnsley doubled looked the more dangerous in the final third and doubled their lead with seven minutes of the first half remaining. Jennings did well to nick the ball from the toe of Omozusi and carry it forward before squaring for Devante Cole who slotted home from eight yards on the angle.
Liverani made a change at the break with Omozusi making way for Mathieu Baudry and shortly after the restart made his third and final change with Dean Cox coming on for Josh Wright in a more central role.
The changes sparked a better spell for the O’s as they looked more promising going forwards with Cox going close after good work from Sawyer on the hour mark.
Legzdins was called into action to make a good save from Berry two minutes later before Orient continued with their pressure and Mooney headed wide from a dangerous McAnuff ball and Cox had strike well saved from distance.
Sawyer looked a threat down the left when he joined in for the O's with some dangerous balls in, but still aside from the Cox effort, Turnbull remained untested in goal for the Tykes.
He was the centre of attention though with 15 minutes to go when he was sent off for handling outside his box. McAnuff put a ball over the top that Batt raced on to and looked to poke past Turnbull who was adjudged to have handled as he blocked the ball.
The decision sparked a change from the home side who took off a striker in Cole to be replaced by sub 'keeper Adam Davies.
The O's have a poor record when playing teams with 10 men this year and despite again having the majority of the ball, failed to put the home side on the back foot or set up a grandstand finish.
BARNSLEY: Turnbull, Berry, Nyatanga, Cranie (C), Hourihane, Hemmings (Lita 72), Jennings, Ramage, Holgate, Bailey, Cole (Davies 75)
SUBS: Brown, Tracy, Digby, Oates, Trotta
Goals: Hourihane 13, Cole 38
Bookings: Hemmings 59,
Red: Turnbull 74
ORIENT: Legzdins, Omozusi (Baudry 45), Sawyer, Vincelot, Cuthbert (C), McAnuff, Lowry, Batt, Wright (Cox 54), Pritchard, Plasmati (Mooney 16)
SUBS: Woods, Lee, Agyemang, Dossena
Bookings: Cox 67, McAnuff 68.
Ref: Mark Brown
Attendance: 8742 (459)