Nathan Redmond scored twice and Manolo Gabbiadini struck a sixth goal in four games as Southampton moved on from their Wembley woe.
The EFL Cup finalists, beaten by Manchester United last Sunday, were trailing after four minutes as Troy Deeney volleyed in for his 100th league goal for Watford. Dusan Tadic equalised and Redmond gave the visitors a deserved half-time lead, only for Stefano Okaka to level 11 minutes from time.
Gabbiadini pounced to punish Heurelho Gomes' error and Redmond struck a fine fourth to give the visitors a win that their pace and movement warranted. There was a nervy conclusion, though, as Watford substitute Abdoulaye Doucoure netted in stoppage time.
Saints' previous Premier League game was the 4-0 win at Sunderland on February 11 and their next is at Tottenham on March 19, so Claude Puel was keen for a victory and got it as his side climbed to 10th place.
Three minutes into the Saints' only Premier League game in 36 days, Okaka set up Deeney to fire home after Younes Kaboul's long throw had caused havoc.
Saints responded positively, and Tadic's run created panic in the Hornets' new back three. The ball broke back to Tadic, who fired low across goal into the corner. Redmond - tipped by manager Claude Puel for an England call-up - started the move which finished with his first league goal since October, surging down the middle before clipping in Tadic's pull-back.
Watford levelled when substitute Isaac Success ran at Cedric Soares and crossed to the near post, where Okaka tucked in. Parity was short lived. Saints substitute Sofiane Boufal's shot from 25 yards bounced in front of Gomes, who did not claim it and Gabbiadini reacted first to score. Then Redmond cut in from the left and unleashed a vicious shot which beat Gomes.
Doucoure tapped in from a yard out, but time ran out for Watford.
Sunday Indo Sport