Town's seven match unbeaten start to the season came to an end at Portman Road against an impressive QPR.
Jamie Mackie struck twice for the Championship leaders inside the first 40 minutes and Heidar Helguson added a third midway through the second-half from the penalty spot.
Carlos Edwards had Town's best chance but pulled his shot wide early in the second-half in a game that the visitors deserved to win once Mackie put them ahead on the half hour.
Town made two changes to the side that took a point at Portsmouth at the weekend. Andros Townsend returned from suspension, Tamas Priskin dropping to the bench with Mark Kennedy coming in for the injured Darren O'Dea.
Helguson tested Marton Fulop inside the first minute but his shot lacked venom.
Paddy Kenny took care of a Grant Leadbitter free-kick at the second attempt, while Kaspars Gorkss headed over the bar from a corner as both sides sounded each other out in the opening exchanges.
Fulop saved at the nearpost from Helguson, the Town No.1 then showing good awareness to cut out Adel Taarabt's dangerous cross.
Rangers got the breakthrough on the half hour, Mackie's shot was initially blocked by Tommy Smith but the ball fell kindly for the former Plymouth striker and he buried it past Fulop into the bottom corner.
It needed a header from Gareth McAuley to clear the danger from Helguson as Rangers threatened a second a minute later.
Akos Buzsaky replaced the injured Alejandro Faurlin for the last 10 minutes of the half, with Rangers beginning to dominate the play and
Mackie grabbed his second four minutes before the interval, making a 40 yard run into Blues' half before driving a low shot past Fulop.
Jason Scotland, who had seen a shot from McAuley deflect wide off the striker's midriff, finished the half with a yellow card for a foul on Kaspars Gorkss.
Roy Keane made two changes at the break, Priskin and Connor Wickham on for Townsend and Luke Hyam, as Blues chased the game with a three man attack.
Wickham made an immediate impact, shrugging off Clint Hill then setting up Carlos Edwards but the midfielder dragged his shot well wide.
Jaime Peters whipped in a cross that Wickham couldn't divert towards goal under pressure, Scotland then sending a tame effort at Kenny.
Fulop kept Blues in the game with two excellent saves on the hour, the first to deny Mackie a hat-trick, then Taarabt's header was beaten out by the Hungarian international. The QPR skipper reluctantly making way for Mikele Leigertwood seconds later in their first change.
Smith became the second Blue to be booked for a foul on Buzsaky as Rangers broke, the Town defender then penalised for a foul on Mackie inside the box. Hogan Ephraim fired a superb shot into the top corner but referee Keith Stroud had blown a split second earlier and pointed to the spot, Helguson did the rest.
Troy Brown replaced Edwards for the last 20 minutes, Peters pushed into midfield and Town continued to press for a way back into the game, Wickham showing strength and touch to carve out an opening for himself but his shot was beaten out by the covering Rangers' defence.
Mackie made way for Tommy Smith for the last 10 minutes and the loan signing from Portsmouth almost scored with his first touch, sliding the ball wide from 10 yards.
Neil Warnock's side saw out the last few minutes with no alarms and the win takes Rangers clear at the top with second placed Cardiff the visitors to Portman Road at the weekend.
Town: Fulop, Peters, McAuley, Smith, Kennedy, Edwards (Brown 70), Leadbitter, Hyam (Priskin 46), Norris, Townsend (Wickham 46), Scotland. Subs not used: Murphy, Eastman, Healy, Hourihane. Booked: Scotland, Smith.
QPR: Kenny, Walker, Gorkss, Connolly, Hill, Faurlin (Buzsaky 36), Taarabt (Leigertwood 60), Derry, Ephraim, Helguson, Mackie (Smith 80). Subs not used: Cerny, Agyemang, German, Parker.