McCarthy broke the deadlock for Wigan in the 19th minute, beating Rob Green with a brilliant volley, but the club was pegged back by Ryan Nelsen's thumping header seven minutes later. Substitute Djibril Cisse gave QPR the lead in the 20th minute but Harry Redknapp’s hopes of achieving that elusive first victory were dashed by McCarthy’s equalizer.
An injury crisis forced Roberto Martinez, also without the suspended Maynor Figueroa, to shuffle his defensive pack with Emmerson Boyce, Ronnie Stam and Adriano Lopez forming a new look back three, while David Jones was deployed in an unfamiliar right wing back position.
Redknapp made just one change to the side that drew at Aston Villa last week, bringing Sean Derry into the midfield to provide some defensive shielding at the expense of Esteban Granero.
Despite being marooned at the foot of the table, Rangers have perked up since Redknapp replaced Mark Hughes in the dugout and started brightly, Shaun Wright-Phillips threatened first, stinging the palms of Ali Al-Habsi with a cross shot from the right in the third minute.
Against the run of play, the Latics snatched the lead courtesy of a stunning strike from McCarthy. An unorthodox free kick from David Jones was tipped over by Green, but from the resulting corner, the goalkeeper was beaten as the Republic of Ireland midfielder reacted to a poor defensive header from Jamie Mackie and rifled a superb first time volley into the far corner.
The visitors regrouped and deservedly restored parity seven minutes later when Nelsen gave Lopez the slip to meet Adel Taraabt’s in swinging corner at the near post and thunder his header past Al-Habsi. Both sides continued to press towards the end of the half with Franco Di Santo missing a sitter at the back post for hosts.
It was one-way traffic after the break as Wigan looked to regain the lead and McCarthy was denied a second goal by a close range save from Green. The R’s shot stopper then had to be on his toes to palm away two long range efforts from Jordi Gomez as Redknapp's men found themselves penned into their own half.
A brief spell of respite came with 20 minutes remaining and QPR took full advantage when Cisse guided Wright-Phillip's low cross past Al-Habsi from 12-yards after the winger had profited from Lopez's misplaced pass deep in Wigan territory.
However, the lead would last just over two minutes. Not for the first time this term, QPR switched off at the back allowing Jean Beausejour to pick out McCarthy, who took advantage of the space provided to control and drive the ball past Green through a crowd of red and white shirts.
It means the west London club has now set a new record of going 16 games without a win since the start of the season and remains rooted to the foot of the table, eight points from safety.