Jesse Lingard gave Ole Gunnar Solskjaer's team the lead at Loftus Road but three goals in six minutes early in the second half ensured a comfortable win for the home side.
Solskjaer's new three-year contract was made public hours before kickoff. He picked a strong team with Brandon Williams, Axel Tuanzebe and Brandon Williams. Nemanja Matic (Nemanja Matic), Mason Greenwood, Mason James, Mason Greenwood, and Lingard all getting starts.
Lingard, who impressed in the win at Derby County on Sunday, didn't need much time to make his mark here. After three minutes, Greenwood passed Facundo Pelistri a pass. His cushioned touch allowed England to score.
United didn't stay ahead for long, with Charlie Austin contributing QPR's equaliser to Lee Wallace's left cross.
Lyndon Dykes, a Scotland striker, was on as a substitute at half-time and put the Championship side ahead. Five minutes later Moses Adubajo made the score 3-1. He cut in the right to fire past Lee Grant from 25 yards.
Dykes got his second goal of the afternoon before an hour had passed. He drilled a shot across Grant and into the corner.
The one highlight for United in the second half was youngster Anthony Elanga's goal from the edge of the area to make it 4-2.
Solskjaer's team continues their preparations for next season with a home friendly against Premier League boys Brentford on Wednesday.