Manager Brendan Rodgers handed midfield duo Youri Tielemans and Harvey Barnes their first outings of the summer as the Foxes shaped up in a 4-3-3 formation from the off, perhaps offering the Blue Army an insight into what tactics the Northern Irishman may deploy in the coming weeks.
City's first real chance of the game came on seven minutes, when Tielemans won the ball in midfield and strode forwards before having his strike blocked just inside the penalty area, with Jamie Vardy peeling away from his marker to make space for the Belgium midfielder.
Eldin Jakupović watched a well-caught half-volley from Lee Wallace sail wide of the target on 17 minutes before Çağlar Söyüncü blocked Moses Odubajo's left-footed attempt and Jakupović saved from Chris Willock as the hosts looked for an early opener in the capital.
Turkey defender Söyüncü was there again to prevent Willock from side-footing in from six yards out, while a defence-splitting pass from Boubakary Soumaré expertly located Vardy, who cushioned the ball into his path with a header, only to drag his effort wide.
Then came another opportunity for the Foxes, as Barnes took a touch, turned and then forced Seny Dieng into a save. Shortly after, Dieng was on hand once more to slide in and get to the ball ahead of Vardy while one-on-one with the forward.
A wayward attempt from Ilias Chair on 33 minutes failed to trouble Jakupović. At the other end, meanwhile, Vardy could not get the desired connection on Portugal full-back Ricardo Pereira's cross from the right flank.
The opener did come just before the interval, however it was QPR who would take the lead on the stroke of half-time as Charlie Austin arrowed an effort into the top corner past Jakupović for 1-0.
At the break, Marc Albrighton - fresh from signing a new contract with the Football Club - replaced Barnes for the second period following the winger's maiden outing of pre-season.
After the lively Willock cannoned a strike onto Jakupović's right-hand post, the R's did double their advantage on 55 minutes as Yoann Barbet nodded in at the far stick.
Searching for a route back into the game, Nigeria midfielder Wilfred Ndidi collected Ricardo's pass and sent a low strike into the arms of Dieng, prior to Ayoze Pérez seeing his dangerous delivery cleared by Rob Dickie and substitute Albrgihton having a cross palmed away by Dieng.
A total of nine changes for City followed just after the hour mark, with only Albrighton and Jakupović remaining on the pitch for the final 30 minutes plus stoppage time.
Academy youngster Ben Nelson was on hand on 68 minutes to get in the way of former Fox George Thomas' strike, while at the other end, Dickie got across to block Kelechi Iheanacho's goal-bound effort just moments later.
Kiernan Dewsbury-Hall was next to have an attempt turned away, and then Dieng was able to gather Hamza Choudhury's placed strike from 20 yards with ease.
City's breakthrough finally arrived on 75 minutes, when Dewsbury-Hall, instrumental thanks to his ball-carrying ability in the build-up, fired home a loose ball in front of over 1,900 Foxes fans that had made the journey to London.
Having witnessed the Academy midfielder score Leicester's first goal of pre-season, the second came not long after as Albrighton clipped a fine pass into Zambian star Patson Daka, who slotted home his maiden strike for his new side to make it 2-2.
A long-ranger from Kamal Sowah had to be held by Dieng in the QPR net, however Mark Warburton's men restored their lead with eight minutes to play after Dickie slammed home from inside the box.
But City's persistence, fuelled by Daka, saw the frontman win a penalty after being hauled down by Dieng, and there was Kelechi Iheanacho to dispatch his spot-kick from 12 yards to seal a 3-3 draw.
Major moment
Although the Foxes were able to recover from a two-goal deficit thanks to strikes from Kiernan Dewsbury-Hall and Patson Daka, the R's regained their lead inside the final 10 minutes after Rob Dickie converted from close range.
However, City did not let their enthusiasm waver and when Daka won a penalty, Kelechi Iheanacho scored his side's third goal of the game - and that's the way it stayed in London.
Who impressed?
Speaking on LCFC TV’s live stream, former Foxes midfielder Dean Hammond said: “He (Patson Daka) didn't have to put his laces through the ball for his goal. He just side-footed it into the net and that'll do great things for his confidence going forward."
Coming up…
Their final pre-season fixture of the summer sees Villarreal visit King Power Stadium on Wednesday (7:45pm kick-off) before their FA Community Shield clash with Manchester City at Wembley Stadium follows three days later (5pm kick-off).