Swansea defender Alan Tate found the back of his own net in the 88th minute to send Leyton Orient into the FA Cup fifth round for the first time in 29 years.
Jimmy Smith headed Russell Slade's men ahead in the 35th minute, but the Swans levelled on the stroke of half-time through Cedric Van der Gun. But the real drama was still to come as Tate diverted a cross from substitute Paul-Jose M'Poku into his own net to send the League One club into the next round.
The visitors opened the scoring against the run of play 10 minutes before the break. Charlie Daniels swung in a free-kick from the right and Smith arrived to plant a header into the net from 12 yards and hand Orient a shock lead.
Yet Swansea responded in style and a spirited rally led them to drawing level on the stroke of half-time. Allen crossed from the left flank and Van der Gun headed home from six yards out.
With two minutes remaining, M'Poku crossed dangerously and Tate inadvertently sent the ball past Yves Ma-Kalambay to send Orient into the fifth round.
Sunday Indo Sport