Wednesday looked a class above in the first half and went in at the interval with a deserved two-goal lead after goals from Jermaine Johnson and Michael Gray.
But Tykes teenager Jacob Butterfield fired his first senior goal for the rejuvenated visitors in the 58th minute and Jon Macken struck a 75th-minute equaliser to send Barnsley's 5,500 travelling fans in crowd of 30,644 into raptures.
Wednesday served notice with their first-half display that they are likely to prove a real handful for the main promotion challengers at Hillsborough this season as they comfortably out-played their neighbours before the break.
But Simon Davey's Barnsley refused to roll over and showed a fighting spirit in the second period that will stand them in good stead this season if they do find themselves in another relegation battle.
Luke Steele's flying one-handed save kept out a thumping drive from James O'Connor in the ninth minute, but the Barnsley goalkeeper was beaten in front of the Tykes' travelling fans moments later.
Gray squeezed past Rob Kozluk down the right wing and his fine deep cross was swept home at the far post right-footed from six yards by the unmarked Johnson.
Gray curled a left-footed free-kick just wide of Steele's post 10 minutes later before Owls goalkeeper Lee Grant performed heroics at the other end when saving with his feet to deny Jon Macken's low shot from 10 yards.
Some of Wednesday's football drew cries of 'ole' and, orchestrated by veteran playmaker Gray, the home side's passing and movement had Barnsley chasing shadows.
Tykes skipper Stephen Foster was lucky not to concede a penalty in the 29th minute when the slippery Francis Jeffers latched on to Gray's clever pass.
But referee Anthony Taylor gave the Barnsley defender the benefit of doubt and awarded a free-kick just outside the box, which came to nothing.
Richard Wood's late lunge denied Macken what would have been a fortuitous equaliser for the visitors before Wednesday were rewarded with the second goal their first-half display merited.
More intricate passing took them deep into Barnsley territory and Marcus Tudgay's deft flick teed up Gray to head home his first goal for Wednesday into the bottom corner from 10 yards.
Grant was quick off his line to thwart Kayode Odejayi just before the break and thrust out a leg to keep out Macken's shot on the turn minutes after the restart.
Wednesday had stepped off the gas early in the second period and were punished for it.
Martin Devaney broke free down the right for the first time and his cross broke kindly in the penalty area for Butterfield, who kept his composure to bury a low drive under Grant's dive in the 58th minute.
Wednesday were stirred into action, but were neither as fluent or accurate with their passing and Barnsley, who had seemed dead and buried in the first half, suddenly found themselves level in the 75th minute through Macken.
Towering strike partner Odejayi flicked on a long free-kick and slack defending allowed Macken to race on into the box and despatch a firm right-footed shot into the bottom corner.