Deeney was involved in the controversial equalizer, heading the ball across the six-yard box where Doucoure arrived late to get in front of goalkeeper Alex McCarthy and push it into the net.
Video assistant referees are being trialled in domestic cup competitions over the next few months, beginning with the FA Cup third-round tie between Brighton & Hove Albion and Crystal Palace earlier this week, but a frustrated Pellegrino now wants to see it rolled out in the English top flight. "We are very sad but we have to accept the rules".
Speaking on the BBC, Sportsmail's Martin Keown commented: 'Doucoure's done a Maradona there, it's like he's gone to high-five the keeper - that's how high his hand was'.
James Ward-Prowse scored Southampton's goals in the 20th and 44th minutes, with Watford jeered off by its own fans at halftime.
Nine Premier League games without a win for Mauricio Pellegrino has seen the Argentine tipped as the next managerial casualty, but his side got off to the flawless start with Ward-Prowse handing them some breathing space in the opening half. "It's the luck of the draw", Deeney told Sky Sports. I have never seen this type of mistake in the Premier League before.
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Swansea felt they should have been awarded a first-half penalty in a 1-1 draw at Newcastle that left the Welsh club rooted to the foot of the table. "Nothing, only talk about this", said Swansea boss Carlos Carvalhal.
"I understand Southampton are unhappy like I was not one time, more than one time when the mistake is against us".
"This is one of the situations VAR will in the future say clear penalty".
VAR can only be used at Premier League stadiums where there is a direct link back to the Premier League studios west of London - where the official operating the system has access to between 12 and 15 camera angles, including four cameras in each goal.
And even Deeney admitted VAR would have ruled out the goal. They'll feel like it's a loss.
"If VAR had come in we probably wouldn't get that but today we got it".