Substitute Darius Henderson scored two late goals as Watford came from behind to beat Southampton and move to the top of the Championship table.
Shittu (right) put Watford ahead with a header
Danny Shittu headed the Hornets ahead before Grzegorz Rasiak toe-poked an equaliser from 18 yards.
Nathan Dyer spectacularly put Saints ahead from outside the area before Henderson guided home Lloyd Doyley's driven low cross at the far post.
And Henderson then tucked the ball home from six yards in injury time.
It was no more than Watford deserved after a superb performance in which they repeatedly tested Saints keeper Kelvin Davis, who made a series of brilliant saves and can consider himself unfortunate to be on the losing side.
Southampton had won their previous two games and would have moved from 19th place to fourth had they held on to their 2-1 advantage.
But on the balance of play a victory would have been a extremely fortunate result for George Burley's side.
Watford, with Nathan Ellington starting in place of Henderson, started briskly - and Davis was soon in action.
Wide players Tommy Smith and Jobi McAnuff were particularly effective, cutting in from the flanks and unsettling the Saints defence.
Davis made sharp saves from each winger within the first 10 minutes, while Gregory Vignal made a brilliant tackle to prevent King from closing in on goal.
King played a superb through ball for Ellington, but again he was thwarted by Davis.
Smith seemed certain to score when the ball came to him six yards from goal but Davis smothered his shot and the keeper then made a brilliant save when Williamson drilled the rebound towards goal from 20 yards.
For all Watford's dominance they almost conceded after 11 minutes when Shittu deflected a free-kick towards his own goal, forcing Poom to make an excellent low save.
But there could have been no complaints when Shittu scored after 42 minutes, converting Smith's precise cross after Davis had come for a cross but made poor contact.
By this stage Davis, excellent in the opening stages, has become increasingly uncertain in his handling and the home side looked a good bet to score the next goal.
However, after a quiet opening half, Rasiak allowed a threaded pass from Dyer to run across his body in injury time before slotting home.
King should have restored his team's advantage within seconds of the restart but, after heading a long clearance from Shittu into space, his early strike was brilliantly saved.
And Davis was soon into action again, denying Ellington after the Hornets striker wrong-footed the Saints defence with a deft turn.
But it was Saints who scored the third, Dyer collecting a ball from substitute Bradley Wright-Phillips before curling the ball across goal with a superb right-footed strike.
And it looked as though it might have earned George Burley's team a scarcely deserved win before Henderson struck twice after 81 and 90 minutes.
Watford manager Aidy Boothroyd:
"I'm delighted with the three points but I'm always searching for perfection and I'm looking for us to make life easier for ourselves.
"We have got some good centre forwards at this club and they are all being pushed. The delivery from set plays from Adam Johnson was also outstanding.
"Last year we didn't have a big enough squad, but this time we are stronger."
Southampton manager George Burley:
"I'm disappointed particularly after we took the lead and it is hard to take. But overall I felt we deserved something from the match.
"Looking at the two sides, they have a strong side and I've got no grumbles about today's performance.
"We had a fair share of possession and I certainly feel we deserved more than what we ended up with."
Watford: Poom, Doyley, DeMerit, Shittu, Stewart, McAnuff (Johnson 59), Mahon, Williamson (Mariappa 82), Smith, King, Ellington (Darius Henderson 66).
Subs Not Used: Lee, Priskin.
Booked: Williamson, Smith, Darius Henderson.
Goals: Shittu 42, Darius Henderson 81, 90.
Southampton: Davis, Vignal, Wright, Thomas, Makin, Dyer, Viafara, Safri, Surman (Ostlund 87), Rasiak (Wright-Phillips 63), John (Euell 46).
Subs Not Used: Bialkowski, Saganowski.
Goals: Rasiak 45, Dyer 69.
Ref: Graham Salisbury (Lancashire).