O'Connor's initial spell at the Pirelli Stadium expired last weekend after Albion's final game of the season against Gillingham.
But with Gary Rowett's side finishing fourth in npower League Two, the deal has been extended to assist their promotion push.
The Brewers face Bradford in the semi-finals over two legs. The first game is at Valley Parade on Thursday night with the return at the Pirelli Stadium on Sunday afternoon.
Should Burton emerge victorious they will take on either Northampton or Cheltenham in the final at Wembley on May 18.
Republic of Ireland Under-21 international right-back O'Connor has made 51 appearances in all competitions during his season-long loan.
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- Gary Rowett