City broke downfield with Schlupp feeding Ulloa who set up Cambiasso, for a precise finish that beat Green inches inside the right hand post.
At the other end a Kranjcar free-kick was deflected narrowly over the bar and there was a scramble in the City area from the resulting corner, but a red shirt eventually managed to clear the danger.
Soon after this Vardy went haring down the right and cut a ball back to Mahrez but in his attempt to beat Green he sent his glancing effort beyond the far post from six yards out.
QPR went close after Kranjcar set up Henry up, bu the delayed his shot long enough for De Laet to come in with a timely tackle.
City held out until the 37th minute, when disaster struck. A penetrating ball from Kranjcar sent Caulker in down the left and his low cross was bundled past Schmeichel by the sliding figure of Morgan as he tried to stop the ball reaching Austin.
City immediately had a great chance to restore the lead as Vardy’s pace saw him one-on-one against Green, but he fired his shot straight at the keeper.
Worse was to come seconds before the half-time whistle. Neither keeper nor defence dealt with a curling cross from Barton. Austin’s header was blocked by Schmeichel, but Fer was on hand to net the rebound from 6 yards.City pushed forward early in the second half and Mahrez forced Green into a save before collecting the rebound and crossing for Vardy to send a looping header onto the crossbar.
Austin then went close with a fierce shot that Schmeichel got down to well.
In the 67th minute City delighted their 1,800 followers with an equaliser. Substitute Albrighton saw his shot blocked by Caulker, but Schlupp latched onto the rebound and lashed home a 22 yarder through a crowded penalty area.
City almost regained the lead when a good attacking spell led to a goal-mouth scramble. The ball fell to Moore after Green saved a Cambiasso shot but he missed his chance to make amends for his own goal, snatching his effort over the bar.
Rangers struck the decisive blow in the 72nd minute after a Barton corner from the right led to another almighty goalmouth scramble. Although substitute Nugent managed to block one shot on the line, Austin was on hand to head into the roof of the net from close in.
City’s best chance to get anything from the game came deep into injury time, but James shot on the turn cleared the bar by inches.
QPR: Green, Suk-Young (Traore 51), Caulker, Onuoha, Isla, Fer, Henry, Barton, Vargas (Mutch 76), Kranjcar (Hoilett 90), Austin. Subs Not Used: McCarthy, Ferdinand, Phillips, Wright-Phillips.
Leicester: Schmeichel, De Laet, Konchesky, Morgan, Wasilewski, James, Vardy, Schlupp, Cambiasso (King 90), Ulloa (Nugent 59), Mahrez (Albrighton 59). Subs Not Used: Hamer, Drinkwater, Moore, Knockaert.
Referee: Mr R East. Attendance: 18,054.