Alcacer has now started the last three games.
"Scoring goals relaxes you, of course, but I always say it's not important who scores but that the team wins," he said. "But, well, I am really happy to score twice -- and also for Andre's [Gomes] brace."
As well as Alcacer and Andre Gomes, there were also two goals for Messi -- who is a joy to play with.
"We know the quality Leo has and what he gives to this team and the club," Alcacer added.
"It's a joy to see him play and to play with him. Few can say 'I played with Messi', so you feel unique to be able to say it."