Robin van Persie and Danny Welbeck netted in quickfire fashion as they set the champions on their way to a 4-1 win in David Moyes's first league game in charge.
Wilfried Bony fired a consolation goal home for the Welsh side on his Premier League debut but it ultimately counted for little, with both United scorers netting again either side of the new man's strike.
|12/1||Swansea City are 12/1 with Bet365 to beat Petrolul Ploiesti 3-1
"It was two minutes of madness, really, and it ended up changing the game.
"If they hadn't scored the second goal then I think we would have had a chance in the second half. That killed it, really, but we gave it everything and we have to accept the defeat and move on.
"It puts things into perspective because we have to get used to losing as well as winning."
Michael Laudrup's side next face Romanian outfit Petrolul Ploiesti for a place in the Europa League proper and Rangel is hoping for a good performance in order to put their heavy loss behind them.
"Thursday's game will help us forget the defeat and it is one of those games that we want to win at home," he added. "I thought we played well [on Saturday] and created lots of chances bt they were clinical and the finishing was the difference in the end."