Watford took the lead after 49 minutes when Lee Williamson picked out Adam Johnson to rise high and head home.
QPR were level within 10 minutes when Stefan Moore turned in a rebound after Dexter Blackstock struck the post.
Mikele Leigertwood was sent off with nine minutes left for a second yellow card, but Camp denied Marlon King and Nathan Ellington as QPR held on.
Watford manager Aidy Boothroyd:
"It was a very open game - too open for my liking. I was disappointed by the way we defended while we were attacking at times.
"I'm also very disappointed with the chances we missed in the first half and I
think QPR will feel the same about the chances they missed.
"Loftus Road is always a difficult place to come and I'm sure QPR will turn
the corner and that John Gregory will get them organised."
QPR: Camp, Timoska, Stewart, Cullip, Barker, Ainsworth (Moore 46), Leigertwood, Bolder, Rowlands, Blackstock, Nardiello (Ephraim 41).
Subs Not Used: Cole, Bignot, Curtis.
Sent Off: Leigertwood (81).
Booked: Bolder, Leigertwood, Cullip.
Goals: Moore 59.
Watford: Poom, Doyley, Shittu, DeMerit (Mariappa 46), Stewart, Smith (McAnuff 73), Williamson, Mahon, Johnson, King, Darius Henderson (Ellington 73).
Subs Not Used: Lee, Priskin.
Booked: Mahon, McAnuff.
Goals: Johnson 49.
Ref: Keith Hill (Hertfordshire).