In just his second match in charge, Postecoglou could only watch on in horror as his side surrendered a two-goal half-time lead, courtesy of Igor Jesus’ double.

Forest wasted a host of chances to extend their lead either side of Cameron Burgess’ goal which gave Swansea hope in the second half.

Zan Vipotnik levelled in added time before Burgess grabbed his second to send the 2013 winners into the last 16.

“I think the lads got a bit comfortable in that moment and you’ve got to know the warning signs,” said former Tottenham boss Postecoglou.

“We had to finish them off and we had plenty of opportunities to do that, and a couple of decisions didn’t go our way.

“Players just thought it would naturally finish that way and we’ve paid a heavy price for that. We need to improve.”