London - Alexis Sanchez helped maintain 10-man Arsenal's Champions League push as his man-of-the-match display condemned Queens Park Rangers to a 2-1 Premier League defeat on Friday.
The Chilean forward went from zero to hero after squandering an early penalty and then putting Arsenal ahead with a 37th-minute header.
Arsenal striker Oliver Giroud was sent off for violent conduct before Sanchez's mazy run carved out a second goal for Tomas Rosicky.
Charlie Austin's late penalty had nerves jangling at the Emirates Stadium, but it was too little, too late for QPR, who fell to a record-equalling ninth straight away defeat.
In a bid to end his side's woes away from Loftus Road, QPR manager Harry Redknapp recalled Rio Ferdinand for the first time since October and he formed part of a new three-man defensive set-up.
But those carefully-laid plans should have been thrown out of the window inside the opening eight minutes.
Former Arsenal left-back Armand Traore, among those called in by Redknapp, tripped the all-action Sanchez for a clear penalty.
Sanchez stepped up instead of regular taker Santi Cazorla, but saw his tame spot-kick pushed out by QPR goalkeeper Rob Green, who also scrambled away the rebound.
Arsenal pressed and probed for an opener, but a combination of last-ditch defending and inaccurate final balls let them down.
Giroud went close from distance before forcing an acrobatic save from Green with a 28th-minute free-kick.
It was one-way traffic and the pressure finally told when Sanchez made amends by heading Arsenal into the lead.
Kieran Gibbs drilled a cross into the box from the left and Sanchez exploited inattentive defending from Traore to head home his 15th goal of the season.
It was the least the hosts deserved. QPR had failed to register a meaningful attempt at goal, but they did sound a note of caution as Steven Caulker headed Eduardo Vargas's cross just wide before the break.
The visitors were given an unexpected helping hand when Giroud was sent off for a moment of madness in the 53rd minute.
The France striker took exception after Nedum Onuoha pushed him from behind as he chased a through-ball and rose from the floor to headbutt the QPR defender right in front of referee Martin Atkinson, who had no option but to send him off.
The angry look on Arsenal manager Arsene Wenger's face as Giroud trudged past him spoke volumes.
The incident threatened to turn the game on its head, but instead Arsenal extended their lead via veteran Czech midfielder Rosicky in the 65th minute.
Sanchez turned creator with a wonderful run and pass that culminated in a delicately-weighted pass for Rosicky, who placed a deflected shot beneath Green to end his nine-month wait for a goal.
The game looked up for QPR, but they were thrown a 79th-minute lifeline when Mathieu Debuchy was harshly adjudged to have tripped substitute Junior Hoilett inside the penalty area.
In-form striker Austin did the rest, slamming the spot-kick down the centre of the goal to register his 12th goal of the campaign.
But besides a Vargas header that was scrambled clear and despite a nervous atmosphere inside the ground, there was to be no grandstand finish as Wenger's team saw out the game with relative ease.