Marlon Harewood headed in a fourth as Bolton rued earlier missed chances by Heidar Helguson and Danny Guthrie.
Radzinski was fortunate to be in the way and divert Helguson's header into the net.
Barnsley conceded another penalty when Shackell fouled Helguson and this time Adel Taarabt scored the spot-kick.
Helguson's penalty was cool, placed low into the corner, giving Rangers a deserved lead.
Helguson volleyed wide on the half-hour mark before Cox headed over from Allan Nielsen's inswinging corner.
But here he was sharing striking duties with Heidar Helguson instead of Francesco Totti.
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Goalkeeper Wayne Hennessey then did well to deny Heidar Helguson when the QPR striker was sent clear.
And Heidar Helguson made it 2-0 just before the hour mark, beating the Reading defence to slot home.
Gary Megson's side had earlier seen a header from Helguson sail over and Guthrie shoot wide when unmarked inside the area.
Bradford goalkeeper Aidan Davison was soon called into action and had to use his feet to keep out Heidar Helguson's shot.
Heidar Helguson's penalty sent them on their way, although Barnsley hit the post through Adam Hammill and Jason Shackell, before Jamie Mackie's tap in.
The flag stayed down - Helguson had indeed been a yard to the good - and left one-on-one with Hahnemann the Icelandic striker slotted home.
Helguson headed over from 15 yards after a fine McBride cross and the American flashed a shot wide at the near post from a well-worked corner.
Helguson missed with a good chance to extend the lead but Smith was not so wasteful, striking home from 18 yards to start the promotion party for Rangers and their supporters.
The visiting side made an enterprising start and Helguson saw a header saved by Scott Loach as QPR looked for the early goal that would set them on the way to sealing promotion.
Fulham boss Chris Coleman opted for the aerial presence of Heidur Helguson and McBride in attack but they were starved of possession and only had one sniff of goal each before the break.
Pennant curled a left-foot shot over as Watford looked to step up a gear, but they suffered a setback when Helguson was injured just before half-time and had to be replaced by Dominic Foley.
The evening started well enough for the home side, who almost took the lead when former Hornets striker Heidar Helguson forced a one-handed save from the highly-rated Scott Loach with a crisp strike from 14 yards.
But they contested an open and entertaining game in the April sunshine at Vicarage Road, with Heidar Helguson crashing an inviting chance into the side netting inside the opening minute after a teasing cross from the ever-involved Taarabt.
City's playmaker David Silva showed his customary sublime control to take Dzeko's low cross and fire in at the near post seven minutes after the break, but QPR leveled on 69 when Bothroyd's header hit teammate Heidar Helguson in the back and deflected past wrongfooted goalkeeper Joe Hart.
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