Swansea lost their unbeaten record as Alfa Semedo struck a late winner for Nottingham Forest at the Liberty Stadium.
Substitute Semedo, on loan from Benfica, struck his first Forest goal five minutes from time to extend his side's unbeaten run to eight games with a 1-0 victory.
Lewis Grabban, a thorn in Swansea's side throughout, broke down the right flank and shook off the attention of Matt Grimes to roll the ball in to Semedo's path and he made no mistake from six yards.
It was no less than Forest deserved against a Swansea side, who stay top of the Sky Bet Championship but would have secured their best ever start to a season with a sixth win from seven games.
Swansea were almost gifted an early opener when Forest goalkeeper Brice Samba hesitated on the ball and Borja Baston came close to profiting.
But Forest were the better side for large parts of the first half and sliced through the Swansea defence after 16 minutes.
Joao Carvalho cleverly flicked Yuri Ribeiro's cross in to Sammy Ameobi's path and the striker forced a full-length save from Freddie Woodman.
Forest went even closer when Ameobi's cross was only cleared as far as Ben Watson 20 yards out.
The midfielder headed the ball back into the box and the stretching Grabban turned it on to the Swansea crossbar.
Samba Sow also sliced wide and Swansea's frustration at failing to build pressure was evident as defenders Jake Bidwell and Mike Van Der Hoorn tried speculative efforts from distance.
The Forest goal was not threatened on either occasion, but Michael Dawson reacted smartly to block Borja's effort at the near post two minutes before half-time.
Forest remained bright after the interval and Grabban latched on to Bersant Celina's back pass to set up Carvalho for a chance which Woodman kicked away at his near post.
Celina was soon substituted after that lapse and Swansea gained some overdue momentum when Andre Ayew headed Bidwell's cross narrowly wide.
But Woodman was again to the rescue to tip Joe Worrall's volley around a post and Joe Rodon, back from international duty after making his debut for Wales, blocked Sow's effort from the resulting corner.
Ayew was becoming an increasing influence on the contest and he tested Samba with a low drive before winning the free-kick which saw the Forest goalkeeper punch clear under pressure.
Forest continued to stand firm and Grabban's strong running and unselfish attitude eventually sealed the points.
