Albion went top with this rampaging win, striker Simon Cox scored his first League goal since a £1.9million move from Swindon while Roman Bednar and Chris Brunt returned to the bench after injury.
I don't believe it! Di Matteo found faults in his team's 5-0 victory over Watford
But was Di Matteo enthused about a game that sent Baggies' fans home beaming with pleasure? Not a bit of it.
He admitted: 'The reason I don't look happy is I am not very happy.'
And why so glum? 'Because I would rather win five games by one goal than one game by five goals.'
First he moaned that a recent two-match barren spell had led to his side being harshly criticised for a goal shortage despite being among the division's top scorers. Then he complained they should have had a couple more penalties.
Next he bleated about Luke Moore's booking, insisting that a push was responsible for him falling over as he went past Watford keeper Scott Loach.
Nor can Albion expect to see a smile on Di Matteo's face any day soon.
'I want to get promoted. Then I'll be a happy man at the end of the season,' he promised.
By comparison, Watford boss Malky Mackay looked on the bright side after Jonas Olsson, Graham Dorrans (penalty), Moore, Gianni Zuiverloon and man of the match Cox inflicted his side's heaviest defeat of the season.
'It was encouraging that even when we went five down I didn't see anybody hiding,' he insisted.
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