David McGoldrick scored the only goal of the game as in-form Nottingham Forest consigned Swansea to only their second home defeat of the season in the Coca-Cola Championship.
Striker McGoldrick smashed home following a scramble in the penalty area in the first half to extend Forest's unbeaten run to 13 matches.
Swansea, who had lost just once in 14 league games ahead of Forest's trip to the Liberty Stadium, bossed possession but were unable to break down a resolute Forest defence.
Billy Davies' Forest, unbeaten away from home this season, are the form side in the division and look capable of mounting a push for automatic promotion.
It was Swansea asking all the questions early on, however. Craig Beattie tried his luck from long range but failed to test Lee Camp.
Dutch forward Cedric Van der Gun had a chance to open the scoring after six minutes but his curled effort flashed over the crossbar.
Van der Gun then produced a dangerous cross for Ashley Williams, but the Wales central defender headed over the bar from just yards out.
Forest's first chance came after 19 minutes when McGoldrick rose to meet a cross from on-loan left-back Nicky Shorey but the striker's header was easily saved by Dorus De Vries.
But it was Swansea who looked the more likely side to open the scoring and Nathan Dyer's curled right-footed strike was palmed away by Camp.
Former Derby goalkeeper Camp was called into action again to keep out a strike from the lively Van der Gun with his feet.
But Forest weathered the storm and they took the lead against the run of play after 34 minutes when McGoldrick volleyed home from 12 yards out after a scramble in the Swansea penalty area.
Andrea Orlandi had an opportunity to restore parity three minutes later, but his free-kick floated over the bar.
Forest almost snatched a second goal on the stroke of half-time, but De Vries produced a fine save to tip Radoslaw Majewski's strike around the post.
Swansea made a bright start to the second half and Camp had to be alert to palm Orlandi's inswinging corner around the post.
Paulo Sousa replaced Beattie with the in-form Lee Trundle seven minutes into the second half in a bid to get his side back into the game.
But, as has been the case on several occasions this season, Swansea were struggling to produce an end product and they were almost caught out once again but Majewski headed straight at De Vries from a Chris Cohen corner.
David Cotterill was presented with an opportunity to open his Swansea account, but the on-loan winger fired wastefully over the bar from the edge of the area 20 minutes from time and Forest held on for three precious points.
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