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QPR started the game on the front foot with Johnson back in the side and causing problems for the Wednesday defence, shooting narrowly wide on two occasions.
It was the visitors who took the lead on 18 minutes, though, when Nuhiu shimmied past a couple of challenges on the edge of the box before firing past Robert Green.
Some nice play from the returning Joey Barton created a couple of half-chances for the hosts, before Onuoha equalised against the run of play, tapping in after a corner.
Moments later QPR were ahead when Johnson was on hand to tap in after an excellent save from Joey Barton's header.
Wednesday will be ruing their defending late on as they somehow go in behind at the break.