However, Southern grabbed an equaliser in the 89th minute and Ormerod popped up soon after as Blackpool bounced back from their dismal 2-1 home defeat to Sheffield Wednesday on Tuesday.
Holloway made three changes to the side that lost to the Owls, with Southern, Gary Taylor-Fletcher and Barry Bannan restored to the starting line-up.
The Seasiders quickly sought to stamp their authority on proceedings and could have led inside six minutea.
Southern crossed dangerously and Adam arrived to plant a firm header towards goal from 12 yards out.
Hornets goalkeeper Scott Loach made the first of several outstanding saves to tip the ball around a post and keep his side on level terms.
Three minutes later, Holloway's men went desperately close again when Bannan flighted in a teasing cross and Southern's powerful header looked destined for the net, but Loach again excelled himself with another brilliant save to keep the ball out.
Watford signalled their threat in the 14th minute when Heidar Helguson drilled a left-foot shot narrowly wide.
Yet Blackpool remained largely dominant and, in the 16th minute, Ormerod drove a right-foot shot wide from 20 yards.
Moments later the impressive Southern hit a fierce left-foot strike from 20 yards which drew another smart parry from Loach.
Moments later, however, Blackpool led when Neal Eardley crossed from the right flank and Adam blasted in a left-foot shot from six yards out.
It was the Scot's 12th goal of an increasingly prolific season and his fourth in his last four appearances.
Watford drew level against the run of the play in the 27th minute when Helguson showed neat skill to reach the byline and cross for Lansbury to tap home his third goal of the season.
Blackpool should have regained the lead in the 30th minute but Adam blazed wastefully over the crossbar from David Vaughan's outswinging corner.
Southern and Adam again went close for Blackpool but they could not add a second before the break.
Three minutes after the restart, Ormerod went close but Loach denied him from 12 yards with another impressive save.
In the 54th minute, Adam had a shot blocked by Lansbury and the visitors cleared the rebound.
Yet the Hornets forged ahead in the 79th minute when Cleverley fired home right-footed from 12 yards.
The response from Blackpool was admirable as they equalised in the 89th minute, Southern converting David Vaughan's fine cross.
And they sealed victory in the closing stages when Ormerod connected with Daniel Nardiello's left-wing cross and fired high into the net from six yards.