The Swans saw their unbeaten start to the season come to an end as they were beaten by ten-man Watford at Vicarage Road.
The home side had the better of a goalless first half, going close on three occasions while Bafe Gomis saw a shot parried away by Heurelho Gomes at the other end.
But Watford broke the deadlock on the hour mark as Odion Ighalo rifled a shot past Lukasz Fabianski.
And despite having to play the final 25 minutes with ten men following Valon Behrami's red card, Watford held firm to earn their first win of the season.
Garry Monk kept faith with the same starting line-up that beat Manchester United before the international break, with August Player of the Month Andre Ayew and joint-top scorer Bafe Gomis both starting.
On the bench, Jefferson Montero was included after missing that victory with a thigh injury while Ki Sung-Yueng was also among the substitutes after a 13,000-mile round trip while on international duty with South Korea.
Watford, beaten 2-0 at Manchester City last time out, made one change to their side as Ikechi Anya came in for Jose Holebas at left-back.
Heurelho Gomes, Allan Nyom, Sebastian Prodl, Craig Cathcart, Ikechi Anya, Valon Behrami, Etienne Capoue, Jose Manuel Jurado, Odion Ighalo (Steven Berghuis, 73), Almen Abdi (Ben Watson, 66), Troy Deeney (Alessandro Diamanti, 82).
Giedrius Arlauskis, Victor Ibarbo, Jose Holebas, Lloyd Dyer.
Lukasz Fabianski, Kyle Naughton, Federico Fernandez, Ashley Williams (capt), Neil Taylor, Jack Cork (Ki Sung-Yueng, 65), Jonjo Shelvey, Gylfi Sigurdsson (Eder, 70), Andre Ayew, Wayne Routledge (Jefferson Montero, 60), Bafe Gomis.
Kristoffer Nordfeldt, Angel Rangel, Kyle Bartley, Marvin Emnes.
After an even opening at Vicarage Road, the home side had the first effort on goal as Sebastian Prodl was teed up on the edge of the box but his fierce half-volley narrowly cleared the crossbar.
Watford's front three of Troy Deeney, Ikechi Anya and Almen Abdi were giving the Swans defence plenty to think about early on and it was Abdi who came mightily close to the opening goal on 18 minutes as his shot took a deflection off Neil Taylor and drop inches wide of the left-hand post.
Just three minutes later the visitors had their first meaningful sight on goal as the in-form Bafe Gomis rolled his marker on the edge of the penalty area before his powerful drive was parried away by Heurelho Gomes.
Back came Watford, however, as Troy Deeney - last season's top scorer - saw his shot fizz past Lukasz Fabianski's left-hand post after some neat build-up.
With six minutes to go until the break, Swansea had their best chance to open the scoring as Andre Ayew robbed the defender near the corner and after his low cross was blocked, Bafe Gomis tried to follow up but his effort was straight at Gomes.
At the other, Fabianski was also called into action late in the half as he did well to save Odion Ighalo's low strike with his legs at the near post.
Half-time: Watford 0 Swans 0
The Swans started the second period on the front foot, dominating possession but without threatening Gomes in the Watford goal - while at the other end, Ighalo managed to steal a yard on Ashley Williams but his low shot was the wrong side of the post.
However, the same player wasn't to be denied just three minutes later as he struck to give Watford the lead.
A cross from the left was touched into his path by Troy Deeney and he coolly slotted past Fabianski from 12 yards out.
That prompted Swans boss Garry Monk to make his first change of the afternoon as Jefferson Montero replaced Wayne Routledge.
But the home side suffered a setback on 65 minutes when they were reduced to ten men, as Valon Behrami was shown a straight red card for a challenge on Andre Ayew.
Ki Sung-Yueng then replaced Jack Cork in the visitors' second change, while Watford introduced Ben Watson in place of Almen Abdi.
Despite being a man light, the hosts came close to a second with 20 minutes remaining as Jose Jurado saw a shot blocked, before Swansea made their third and final change as Eder replaced Gylfi Sigurdsson.
The Swans tried to find a way back into the game in the closing stages - Jonjo Shelvey going close with a long-rang strike and Federico Fernandez heading wide - but the hosts held firm to earn their first league win of the season.