Barnsley looked relatively comfortable in a goalless first half but the closest
they came to finding the net was a smart shot from former Rams midfielder Tomasz Cywka that home goalkeeper Adam Legzdins did well to turn over the top.
Derby had made a confident start and in the ninth minute striker Conor Sammon produced a neat turn and shot 10 yards out but the ball flew over Steele's crossbar.
Tykes boss Keith Hill had made four changes from the Barnsley side that lost 1-0 at Hull at the weekend, and one of the men recalled to the starting line-up, striker Chris Dagnall, got on the end of a nice 13th minute break down the left but sent his 12-yard shot narrowly wide.
The Derby fans urged their side forward and after 23 minutes a long-range
effort from Jeff Hendrick brought a fine save from Luke Steele.
Cywka was then thwarted by Legzdins, but the Rams roused themselves as
half-time approached and Steele had to make a couple of notable stops to deny both Will Hughes and Jeff Hendrick.
The first real chance of the second half was created by Barnsley, Cywka's low
drive being deflected into the side netting.
Derby had appeals for a 55th-minute penalty waved away by referee David Coote after Craig Bryson tumbled to the turf and seconds later Barnsley broke to the other end and Dagnall's left-footed shot was well parried by Legzdins.
Steele then produced a great reaction save to keep out Paul Coutts' deflected
free-kick, but he could not prevent O'Connor from finally making the
breakthrough before Nathan Tyson settled the issue with his sublime late strike.