Martin Rowlands' penalty gave QPR an early lead, with Damion Stewart heading home a corner for the visitors' second.
Rowlands burst into the area and fired in a third on 40 minutes, before Watford's Damien Francis finished from close range early in the second half.
QPR substitute Buzsaky stole in and rounded Richard Lee before angling home a drive to make it 4-1, with Danny Shittu poking in Watford's second goal.
Watford manager Adrian Boothroyd:
"I was pleased with our attacking play but not some of the defending. It was schoolboy stuff.
"There was no ranting or raving at half-time, we just talked about what we had to do to. We got back into it and then left ourselves open."
QPR manager Luigi De Canio:
"In the dressing room we only talk about our opponents, not what might happen tomorrow or in January.
"Everyone needs to do his duty. That is a sign of maturity and each one of these players has that."
Watford: Lee, Doyley (O'Toole 79), DeMerit, Jackson (Shittu 46), Stewart, Smith, Williamson, Francis, McAnuff, Darius Henderson, Ellington (King 68).
Subs Not Used: Mariappa, Ainsworth.
Booked: Doyley, Smith.
Goals: Francis 52, Shittu 84.
QPR: Camp, Barker, Rehman, Stewart, Malcolm, Bolder, Rowlands, Ainsworth (Vine 64), Balanta (Buzsaky 73), Nygaard (Walton 90), Blackstock.
Subs Not Used: Cole, Moore.
Booked: Nygaard, Barker.
Goals: Rowlands 13 pen, Stewart 29, Rowlands 40, Buzsaky 80.
Att: 18,698
Ref: Chris Foy (Merseyside).
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