Arsenal beat Manchester United 2-1 to reach the FA Cup semi-finals . Goal hero Danny Welbeck left Old Trafford in a £16m deal the second half . Louis van Gaal did not expect his former striker to start on Monday night . Welbeck grabbed the winner and celebrated with the travelling supporters . Angel di Maria was sent off , with the Dutchman admitting that his player was not 'smart ' to touch referee Michael Oliver . Van Gaal also described the result as a 'big blow ' for his side .
Arsenal beat Manchester United 2-1 to reach the FA Cup semi-finals . Goal hero Danny Welbeck left Old Trafford in a £16m deal last summer . Louis van Gaal did not expect his former striker to start on Monday night . Welbeck grabbed the winner and celebrated with the travelling supporters . Angel di Maria was sent off , with the Dutchman admitting that his player was not 'smart ' to touch referee Michael Oliver . Van Gaal also described the result as a 'big blow ' for his side .