Missile: Danny Graham was targeted as he celebrated his goal for Watford
Watford midfielder Stephen McGinn suffered a gashed head after he was struck by a missile thrown by Rangers supporters just after Danny Graham had scored his second goal of the night and 12th of the season.
McGinn continued after treatment but was substituted 27 minutes later. A bottle also narrowly missed Graham.
Watford manager Malky Mackay said:'I'm not sure how it happened but Stephen has got a large cut, his eyeis closed and he's got a concussion.
'The fourth official told me threebottles of beer were thrown from the top tier but until such time Ihear categorically what has happened I don't want to comment on whetherwe will look to take action.'
Rangers would have equalled a recordof 20 League games without defeat had they not been beaten last night,and superstitious manager Neil Warnock has worn his training
shorts for all their Championship games this season and vowed not to change until his side lost.
But Graham's double means Warnockcan finally add a pair of trousers to his match-day wardrobe afterRangers lost their first game of the campaign.
Warnock said: 'I'm glad I can put mytrackie bottoms on now. I'll have my long johns on as well now it'swinter. It'll be a lot more convenient.
Record breaker: Danny Graham scores Watford's first to set up QPR's first defeat in the league this season
'We've got a run of tough games ahead, a lot of them are away. So if we can be there or thereabouts after the next 10 games or so I'll be happy.
'We're disappointed to lose our unbeaten run but if you had told me we'd get to December without losing, I'd have called you crazy.'
Heidar Helguson forced Watford keeper Scott Loach into an excellent save with a wellstruck shot in the opening five minutes as Rangers started brightly.
But Warnock warned his side about Graham before the defeat, so he was livid when the striker was given the freedom of the six-yard box to fire home Andy Taylor's cross in the 26th minute.
What a spectacle: Outraged QPR boss Neil Warnock vents his anger towards the assistant referee
Watford doubled their lead four minuteslater as Jordon Mutch's inswinging left-footed cross flew over everyonebefore arrowing into the net.
Clint Hill saved Warnock's side from going three down before halftime with a goal-saving block from Mutch's close-range effort after a rapid Watford breakaway.
But Warnock's half-time rocket had zero effect as Graham hit Watford's third just three minutes into the second period after McGinn's cheeky back heel.
No way through: It was a frustrating night for the hosts and star midfielder Adel Taarabt
A disastrous night could have been so much worse for the West London side as Shaun Derry cleared another Mutch effort off the line before keeper Paddy Kenny made a point-blank stop to prevent Graham scoring a hat-trick.
Former Watford striker Tommy Smith reduced the deficit in the 89th minute, but Warnock knew it was scant consolation.
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Explore more:People: Neil Warnock, Tommy Smith, Danny Graham Places: London