Jesse Lingard scored twice after being brought off the bench to help Manchester United recover from two goals down in their 2-2 draw with Burnley on Tuesday.
The Red Devils were facing just a second defeat at Old Trafford in 43 outings, and a first to the Clarets since 1962, before Lingard bagged goals at the start and end of the second half.
Ashley Young gave away an early free kick which Jeff Hendrick swung in and, after the Red Devils failed to clear their lines, Barnes was there to profit as he turned it home.
United were left stunned soon after, however, as Steven Defour expertly sent a free kick flying past De Gea’s reach from 30 yards to double his side’s tally.
As the match entered the final 10 minutes there was no real change to the flow of the game, with the Red Devils bossing possession but lacking creativity, failing to muster another shot on goal until Lingard’s late leveller.