The Bees dominated early on and made the breakthrough when O’Connor smashed home from 12 yards after James Tunnicliffe had fouled Clayton Donaldson.
Ben Strevens hit the post for the Chairboys and Andy Sandell fired in a wicked free-kick in the closing stages but Richard Lee was equal to it.
After starting the strongest the Bees struck when Myles Weston slid Donaldson through and, as the striker cut across the left of the area, Tunnicliffe clumsily bundled him over.
Captain O’Connor confidently stepped up and thumped the ball low to Bull’s left to send the packed away end into raptures after 36 minutes.
Gary Waddock’s men needed inspiration and their best chance came as Sandell whipped a free-kick round the wall with nine minutes remaining, only for Lee to brilliantly push it to safety.