A quick-fire double from Robert Earnshaw put them in control before Dexter Blackstock made it a comfortable lead from the penalty spot against his former club.
Chris Cohen put the game beyond doubt with a 25-yard strike at the start of the second half and James Perch completed the rout as the Reds joined Newcastle on 52 points at the division's summit.
One more goal would have actually seen Davies' side usurp the Magpies at the top on goals scored.
"Promotion - not a chance," said the Scot. "At the moment we have achieved nothing.
"People can talk all they like, but there are too many sporting moments in days gone by where teams or individuals have blown it at the final hurdle. It can happen.
"We can't afford to do anything except prepare for the next match and keep picking up points.
"This is a good side and we are still learning and working hard. We were clinical tonight and it is an important two points gained over West Brom.
"But until it's over, I'm sorry there are a lot of teams outside the top six that will still believe they can catch us - and they can."
Mick Harford endured a torrid return to the City Ground in only his second game as caretaker boss of QPR.
A fortnight ago Harford was expecting to come back to Forest as assistant to another former Reds manager Paul Hart.
But Hart made a shock exit from the London club after just five games in charge and Harford was promoted to the helm for the 2-2 draw at Blackpool 10 days ago.
Harford, acting manager at Forest in 2004 following the departure of his old mentor Joe Kinnear, admitted his side had been roundly beaten.
"That kind of performance is not acceptable and the players know that," he said.
"After getting through the first 20 minutes, we gave away three easy goals and never had a shot on target in the first half - and for a QPR side that is a sin because we have some very good players.
"But we knew it would be tough. We told them before the game and we knew we would be playing a high-energy team that has some very good players within their framework.
"On the night we just couldn't deal with what they threw at us."