Tony Mowbray felt the game drifted away from Rovers after his side put themselves in such a good position.
Early goals from Bradley Dack and then Danny Graham put Rovers in command after only eight minutes of play at a crisp Griffin Park.
But the hosts quickly responded through the impressive Said Benrahma, before second half goals from Neal Maupay, substitute Sergi Canos and a brace from Ollie Watkins finished the visitors off.
However, the scoreline wasn't a true reflection of the performance from Mowbray's men, who had their chances to earn victory, particularly in the first half.
“From being very dominant, we gave away some really poor goals," Mowbray reflected after the game.
"The second goal was the killer really. Nobody went to close the man down on the edge of the box.
“We gave away some poor goals. We had to chase the game and then it ran away from us.
“I thought we were capable of scoring five goals ourselves, to be honest. The game ended up drifting away from us after what was a pretty good first half performance.
“I’ve said to the players that we’ll analyse things on Monday and move on to the next game."