Andre Gray's goal for Watford was his fifth of the season
Swansea City will face Barnsley in the Championship play-offs after ending the regular season with a defeat at promoted Watford.
The Swans shaded a goalless first half with Andre Ayew and Matt Grimes denied by Hornets goalkeeper Ben Foster.
Andre Gray instinctively turned in Ken Sema's cross to put Watford ahead before Isaac Success added a second late on with a fabulous strike.
The result means Swansea finish fourth in the table, with Watford second.
Meanwhile, Barnsley drew with champions Norwich City to leapfrog Bournemouth - who lost at home to Stoke - into fifth place.
That means Barnsley will host Swansea in the first leg of their play-off semi-final on Monday, 17 May, with the return fixture at the Liberty Stadium the following Saturday.
Having secured their instant return to the Premier League with two games to spare, Watford were welcomed on to the pitch at Vicarage Road with fireworks and yellow ticker tape.
- EFL ups and downs as it happened
And with lifelong fan and former owner Sir Elton John watching from the stands, this felt like a celebration for the Hornets, even without a home crowd.
They created the first chance of the game, Sema breaking down the left wing and crossing to Philip Zinckernagel, whose first-time shot swerved narrowly wide.
Swansea had long been guaranteed their play-off place but, with their opponents dependent on their final league position, this was more than a mere training exercise.
Top scorer Ayew was restored to the starting line-up after injury and he came close to opening the scoring with a powerful seventh-minute shot which was blocked by Foster.
Swans captain Grimes forced Foster into another save with a firm hit from 20 yards and, despite starting the second half brightly with Liam Cullen firing over the bar, the visitors fell behind soon afterwards with a somewhat fortuitous goal.
Sir Elton John has been involved with Watford in various capacities since becoming chairman in 1976
Sema whipped in a dangerous cross from the left, which took a deflection off Swansea defender Marc Guehi before hitting Gray and flying into the net.
The visitors continued to create chances after falling behind but, careful not to over-exert themselves with the play-offs looming, important first-team players such as Grimes, Ayew, Conor Hourihane and Jamal Lowe were replaced.
Watford then wrapped up victory in the closing stages as Success lashed a fierce shot into the top corner to bring to a fitting end to a triumphant season which saw them return to the Premier League at the first attempt.
Swansea City head coach Steve Cooper told BBC Radio Wales:
"You're always disappointed to lose. I quite liked us in the game - I didn't think it was a 2-0 game.
"We didn't threaten the goal enough, particularly in the second half, and they did. That was where the game was won and lost.
"We finished fourth, which I think is an excellent return, and now we can look forward to the play-offs.
"Going into these play-offs, we should fear nothing and go for it."
- Line-upsMatch StatsLive Text
Line-upsWatford
Formation 4-3-3
1Foster32Navarro27Kabasele15Cathcart17Lazaar7Zinckernagel28C Sánchez16Gosling22Success18Gray12Sema
- 1Foster32Navarro27Kabasele15Cathcart17Lazaar7ZinckernagelSubstituted forHughesat 65'minutes28C SánchezSubstituted forJoão Pedroat 65'minutes16GoslingSubstituted forWilmotat 82'minutes22Success18GraySubstituted forDeeneyat 72'minutes12SemaSubstituted forMasinaat 82'minutes
Substitutes
- 5Troost-Ekong6Wilmot9Deeney10João Pedro11Masina19Hughes25Perica26Bachmann31Sierralta
Swansea
Formation 4-3-3
1Woodman23Roberts2Bennett5Guehi24Bidwell6Fulton8Grimes14Hourihane10A Ayew20Cullen9Lowe
- 1Woodman23Roberts2Bennett5Guehi24Bidwell6Fulton8GrimesSubstituted forSmithat 66'minutes14HourihaneSubstituted forWhittakerat 77'minutes10A AyewSubstituted forCooperat 65'minutes20CullenSubstituted forRoutledgeat 66'minutes9LoweSubstituted forDhandaat 66'minutes
Substitutes
- 3Manning7Smith15Routledge17Whittaker18Hamer21Dhanda22Latibeaudiere26Naughton31Cooper
Referee:Geoff EltringhamMatch StatsHome TeamWatfordAway TeamSwanseaPossessionHome48%Away52%ShotsHome10Away15Shots on TargetHome3Away2CornersHome3Away8FoulsHome12Away6Live TextPost update
Match ends, Watford 2, Swansea City 0.
90'+3'Full Time
Second Half ends, Watford 2, Swansea City 0.
90'+3'Post update
Attempt missed. Yan Dhanda (Swansea City) right footed shot from outside the box is too high from a direct free kick.
90'+2'Post update
Jake Bidwell (Swansea City) wins a free kick in the attacking half.
90'+2'Post update
Foul by Will Hughes (Watford).
87'goalGoal!
Goal! Watford 2, Swansea City 0. Isaac Success (Watford) right footed shot from the right side of the box to the top left corner. Assisted by Marc Navarro.
85'Post update
Jay Fulton (Swansea City) wins a free kick on the right wing.
85'Post update
Foul by Ben Wilmot (Watford).
84'Post update
Corner, Watford. Conceded by Freddie Woodman.
84'Post update
Attempt saved. Achraf Lazaar (Watford) left footed shot from the left side of the box is saved in the top centre of the goal. Assisted by João Pedro.
82'Substitution
Substitution, Watford. Ben Wilmot replaces Dan Gosling.
82'Substitution
Substitution, Watford. Adam Masina replaces Ken Sema.
79'Post update
Attempt missed. Yan Dhanda (Swansea City) right footed shot from the right side of the box is high and wide to the right. Assisted by Wayne Routledge following a corner.
79'Post update
Corner, Swansea City. Conceded by Will Hughes.
79'Post update
Corner, Swansea City. Conceded by Dan Gosling.
79'Post update
Attempt blocked. Oliver Cooper (Swansea City) right footed shot from outside the box is blocked. Assisted by Korey Smith.
78'Post update
Corner, Swansea City. Conceded by Christian Kabasele.
78'Post update
Attempt blocked. Wayne Routledge (Swansea City) right footed shot from the centre of the box is blocked. Assisted by Yan Dhanda.
77'Substitution
Substitution, Swansea City. Morgan Whittaker replaces Conor Hourihane.
75'Post update
Attempt missed. Yan Dhanda (Swansea City) right footed shot from the left side of the box is close, but misses to the right. Assisted by Conor Hourihane.
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Source: bbc.com