Brentford got a penalty in the tenth minute when Bryan Mbeumo collapsed in the penalty area.
Ivan Toney scored 1-0.
Ten minutes later Emiliano Marcondes scored the second.
Swansea started chasing goals - but had a hard time getting holes at Brentford.
It got even harder when Jay Fulton was sent off with barely half an hour left to play.
Brentford held off and won 2-0.
Thus, the club is ready for the Premier League next season.
That place is worth two billion kroner, according to the BBC.
Sweden gets another player in the Premier League if midfielder Pontus Jansson stays at the club. Jansson was substituted in the 79th minute, it is unclear if he is injured.