FIVE-STAR Albion stormed back to the Coca-Cola Championship summit as they made a mockery of their recent troubles in front of goal.
The Baggies, who failed to score in four of their last six games, were never in danger from the moment Jonas Olsson headed his third goal of the season in the fifth minute.
Graham Dorrans doubled the lead from the penalty spot on 17 before Luke Moore's first goal in nine games four minutes after the break effectively put the game out of the Hornets' reach.
Watford headed to The Hawthorns six unbeaten on the road but that record was truly put to the sword when Albion added goals four and five inside five minutes.
Gianni Zuiverloon netted his first league goal for the club with a fine individual strike on 64 before Simon Cox opened his Baggies league account with a fierce long-range drive.
Roberto Di Matteo rang two changes from the goalless draw at Coventry as he reverted to a 4-4-2 formation. Summer signing Cox was handed only his second Championship start of the term while Filipe Teixeira was granted his first.
The men to make way were Youssouf Mulumbu, who lost his ever-present league record to a knee injury, and Robert Koren, who dropped to the bench.
Roman Bednar and Chris Brunt were only fit enough to be named as subs on their returns from back and calf injuries respectively.
Albion started the day in fourth place after Leicester's impressive win at QPR last night but still had the carrot of knowing a victory would propel them to the top of the table.
Malky Mackay made one change, with John Eustace replacing Ross Jenkins, while Albion old boy Nathan Ellington started on the bench.
Albion got off to the perfect start when they bucked a worrying trend by opening the scoring for the first time in six home games.
After Lee Hodson had been booked for upending Joe Mattock, Dorrans swung the ensuing free-kick into the box and Olsson towered above Craig Cathcart at the far post to head past Scott Loach.
Albion's opener proved the only effort on goal of the first 15 minutes but there was a nice pattern to the game, with both teams looking comfortable in possession.
The Baggies continued to play with patience and doubled their lead on 17.
Referee Nigel Miller pointed to the spot after Moore was sent sprawling by Hornets skipper Adrian Mariappa after controlling Olsson's exquisite ball over the top.
Dorrans made no mistake from the spot, tucking away as perfect a penalty as you will see to notch his first league goal for the club.
Watford did not record an effort at goal until the 21st minute when Danny Graham was well off target with a speculative 25-yard drive.
Henri Lansbury was similarly unsuccessful from distance two minutes later after a neat Watford counter-attack.
Albion were quite happy to sit on their lead and looked composed and it was only a mistake on their own part which almost let Watford in.
A mix-up between goalscorers Olsson and Dorrans resulted in the ball sitting up perfectly for Graham just inside the box and the lone striker fizzed a right-footed volley just over.
Albion thought they'd won another penalty on 33 when Moore raced onto the lively Cox's sublime throughball, shrugged off Mariappa and went sprawling over on-rushing keeper Loach.
But referee Miller incensed the Albion striker by awarding the visitors a free-kick and booking him for simulation. TV replays suggested the decision was very harsh.
Watford recorded their best effort on goal five minutes later when Mariappa headed a good chance over after Don Cowie's corner had been nodded goalwards by Cathcart.
Albion almost caught the Hornets cold again at the start of the second half when, just 40 seconds in, Olsson saw a near-post header from Dorrans' corner headed off the line by Hodson.
But Watford should have pulled one back on 48.
Jon Harley shrugged off Abdoulaye Meite and advanced into the penalty area and his low cross, which took a deflection off Mattock's outstretched boot, was stabbed wastefully wide by Graham at the far post.
Albion missed just as golden an opportunity seconds later when Mattock's cross bounced perfectly for Cox who directed an instinctive header over from eight yards.
The second 45 had started at a frenetic pace and Albion gave themselves some breathing space when they made it 3-0 in the 49th minute.
Only a fine Loach block denied Moore after the former Villa man had shrugged off the attentions of both Hodson and Mariappa to seize Cox's slide-rule pass.
But Moore pounced on the rebound and composed himself before rifling a terrific right-footed shot inside the far post from an acute angle.
Watford now had to go for broke and Scott Carson, who had barely touched the ball, was relieved to see Cleverley curl a 16-yard shot inches wide of his far post.
Albion were in complete control but it was the Vicarage Road club who recorded the next shot at goal - and their first on target - when Lansbury volleyed fiercely at Carson from 20 yards.
It should have been 4-0 on 63 when Zuiverloon did brilliantly to spin past Loach and unselfishly tee up Thomas, but the winger's goalbound shot was brilliantly blocked on the line by Hodson.
However, Albion did notch again a minute later - and how.
Zuiverloon charged past Cathcart and Lloyd Doyley before planting an unstoppable shot inside the far post from the tightest of angles.
There was still only 69 minutes on the clock when Cox crowned a fine display by making it five.
Moore managed to lay a high ball into his strike partner's path and Cox lashed home first time from 25 yards. Loach managed to get an arm to it but the shot's venom proved too much for him.
Watford rallied briefly and Carson had to get down smartly to hold onto sub Ellington's 15-yard drive.
But back came Albion and Moore probably should have done better when he stabbed wide from Dorrans' exquisite centre.
The chances kept coming during the closing stages, with the industrious Teixeira twice shooting inches wide.
To their credit, Watford kept plugging away and Mariappa wasn't too far away with a header from Lansbury's centre.
Carson had to pull off his only save of note in the third minute of stoppage time when he brilliantly tipped over Ellington's powerful header from another Lansbury delivery.
ALBION (4-4-2): Carson; Zuiverloon, Meite, Olsson, Mattock; Teixeira, Dorrans, Jara, Thomas (Brunt 64); Cox, Moore. Subs not used: Kiely (gk), Bednar, Martis, Koren, Wood, Cech.
WATFORD (4-5-1): Loach; Hodson, Mariappa, Cathcart, Doyley; Cleverley, Lansbury, Eustace (Severin 85), Cowie (Helguson 52), Harley; Graham (Ellington 64). Subs not used: Bond (gk), Henderson, Sadler, Bryan.
GOALS: ALBION - Olsson (5), Dorrans (18 pen), Moore (49), Zuiverloon (64), Cox (69).
BOOKINGS: ALBION - Moore (simulation 33). WATFORD - Hodson (foul 5).
REFEREE: N Miller (County Durham).
ALBION STARMAN: Simon Cox.