Boss Nathan Jones named an unchanged starting eleven from Friday's 2-0 win at Huddersfield, with Pelly-Ruddock Mpanzu making his 250th appearance for the club and Dan Potts racking up his 150th.
Rangers enjoyed the lion's share of the possession in the opening 15 minutes, but it was the Town who drew first blood from the penalty spot in the 20th minute.
A crunching tackle by Andrew Shinnie on Luke Amos moments earlier had set the tone, with Elliot Lee breaking onto the loose ball and releasing Harry Cornick into a dangerous position on the right.
The forward may have shot instead of attempting to cut the ball inside, but even though that attack petered out, when Lee and Luke Berry combined to set the rampaging right-back James Bree into the box, the Town seemed destined to register their first attempt on goal.
Rangers left-back Ryan Manning took the Aston Villa loanee's leg away as he prepared to shoot, and referee Stephen Martin had no hesitation in pointing to the spot. Top scorer Collins similarly showed no complacency in sending Joe Lumley the wrong way from 12 yards.
Two minutes later the Republic of Ireland striker almost turned provider, sending a low cross towards Lee, but the forward couldn't get enough purchase on his effort as he slid in and the ball squirmed the wrong side of the far post.
The visitors thought they'd created an opening just after the half-hour, but Ilias Chair couldn't climb high enough to get a proper header on Osman Kakay's cross from the right.
The same player, moved from centre-half to right-back when Angel Rangel was carried off on a stretcher in the early stages, delivered another inviting centre soon after, and although Eberechi Eze brought this one under control, his shot was deflected into the side-netting.
Chair fired a 25-yarder straight at Sluga, but the Hatters created the next best chance of the opening half, with time almost up, as Lee, Potts and Berry exchanged passes on the left to set the former into the box, but his trademark curler was too close to Lumley.
Town thought they had doubled the advantage within 90 seconds of the restart, but Potts was penalised for pushing as he climbed to head Bree's corner past Lumley.
Another Bree set-piece, this time a free-kick from deeper after a surging run from Berry was brought to an illegal halt, saw Bradley head back across goal for Potts, but the left-back couldn't get enough power behind his header to trouble Lumley.
Then, just before the hour, Sluga had to be alert to repel a bullet header from QPR skipper Yohann Barbet, who met Manning's free-kick 12 yards out after Mpanzu had been shown a yellow card for pulling back Bright Osayi-Samuel in midfield.
It was the Rangers wideman whose pace down the left created the equaliser on 65 minutes, Ball arriving in the penalty area to sidefoot the former Blackpool flyer's cut-back into the bottom corner.
Martin Cranie was introduced for Lee in the drinks break that followed the goal, and it was his calm pass out of the Town penalty area to Berry that allowed the midfielder to release Cornick with a perfectly threaded ball into the Rangers half.
Cornick's left footed shot was deflected wide, then, from Bree's left-wing corner and Bradley's knock-down, the forward's next attempt was also diverted for another corner before Shinnie fired high over the bar.
Rangers were threatening, however, and Sluga had to scramble across his line to turn the ball around his left post after spilling a cross and seeing the loose ball deflected goalward by Mpanzu.
With Danny Hylton, Kazenga LuaLua and George Moncur waiting to come on, Potts, Collins and Cornick linked up on the left and the latter broke into the Rangers box, but his stabbed shot was well off target as he came under pressure from a back-tracking defender.
Hylton then crossed low from the right and Potts fired a left-footer at goal, but Lumley produced a fine save to deny the full-back a winner.
With Hull having been hammered 8-0 at Wigan and Charlton not playing until tomorrow, the result leaves Town level on points with the Tigers - who we visit on Saturday - and a point adrift of the Addicks.
TOWN: Sluga, Bree, Carter-Vickers, Bradley (C), Potts, Mpanzu, Shinnie (Moncur 83), Berry, Lee (Cranie 67); Cornick (LuaLua 83), Collins (Hylton 82).
Substitutes: Shea, Tunnicliffe, McManaman, Butterfield, Kioso.
Goals: Collins (pen) 20
QPR: Lumley, Rangel (Masterson 11), Manning, Barbet (C), Cameron, Kakay, Ball, Amos, Eze; Chair, Osayi-Samuel
Substitutes: Kelly, Kane, Wallace, Shodipo, Oteh, Bettache, Gubbins, Clarke
Goals: Ball 65
Referee: Stephen Martin