Jurgen Klopp's side looked to be coasting to victory on Spanish soil when they led 3-0 at the break, only to suffer a worrying second-half collapse that once again raised questions over their defensive deficiencies.
Wissam Ben Yedder scored twice before Guido Pizarro struck a dramatic late equaliser to rescue a point for Sevilla and deny a shell-shocked Liverpool from qualifying for the knockout stages.
Coutinho put the capitulation down to the players losing focus after such an impressive first half, something they can ill-afford to let happen again in the future.
"It wasn't a good result, we almost felt like we do after a defeat," the Brazil international told Liverpool's official website.
"We had a great first half and then in the second half we let everything unravel and so we were all feeling very frustrated.
"We have to stay awake all the time, 100 per cent. I think that the first half, the way we went into the game, we have to go into the second half [like that] too.