Swansea overcame struggling Middlesbrough 1-0 at the Liberty Stadium on Sunday to keep their promotion dreams alive.
England Under-21 international Scott Sinclair's strike six minutes from time, his 12th in the last 16 games for the Swans, proved to be the difference.
Swansea now trail second-placed Queens Park Rangers by three points and four points behind leaders Cardiff City at the top of the Championship table.
Swansea had dominated proceedings from start to finish, only to waste a string of chances through Nathan Dyer, Angel Rangel and Joe Allen.
A draw seemed likely until one-time Chelsea winger Sinclair cut inside and fired in a low shot into the bottom corner of the net that handed them the three points.
For the visitors, their best two openings fell to Gary O'Neil and Scott McDonald, but neither could prevent their team from going down to their second defeat since Tony Mowbray took over from Gordon Strachan four matches ago.
Goal difference now separates Middlesbrough from Bristol City and Crystal Palace in the relegation zone.