Rangers went into the match unbeaten in four games but had no answer to a second-half onslaught from the Tractor Boys.
But despite a seventh-minute scare when goalkeeper Paul Jones spilt a Matthew Richards free-kick, the hosts dominated the early exchanges.
At the centre of most of their attacks was Australian midfielder Nick Ward, who hit a 25-yard screamer just over the bar on eight minutes.
But once the visitors settled into the game they began to express themselves. Teenager Billy Clarke looked lively up-front and he forced a good save out of Jones after linking up with Richards on 20 minutes.
Although Dexter Blackstock should have put QPR in front after 35 minutes when he was put clean through on goal only to see his attempted finish stopped, Ipswich had two gilt-edged chances of their own before half-time.
Jason De Vos missed a sitter which fell to him just six yards out and then Clarke could only hit the bar after being put through by Alan Lee.
The visitors made the brighter start to the second half - so manager Jim Magilton would have been screaming at on-loan Mark Noble for not taking his 56th-minute chance, before Rangers opened the scoring.
Noble cut inside from the right but passed a weak right-footed shot into the hands of Jones rather than hitting it with his left foot.
Kevin Gallen was duly on hand at the other end to scramble the ball over the line after being found by Blackstock, to give QPR the lead while Ipswich defender Alex Bruce was off the field receiving treatment.
But the celebrations were short-lived as, four minutes later, Gavin Williams broke into the QPR box and appeared to dive over the tackle of Damion Stewart.
However, referee Lee Mason awarded the penalty and Simon Walton, on-loan from Charlton, slotted home.
Ipswich had to wait only six minutes until their next goal came, but not before Williams was unlucky when his volley direct from a corner hit the post.
Gallen cleared but De Vos was left unmarked at the resulting corner to tap home.
Gary Waddock's men failed to come up with a response and the visitors wrapped up the points four minutes from time when Dean Bowditch nodded home after Jones blocked a Williams shot.