AFC Bournemouth has appointed Scott Parker as their new head coach after he left his post at Fulham by mutual consent.
Michael Keane was injured in a clash of heads with teammate Idrissa Gueye as both players jumped to clear the ball late in the game.
Callum Wilson, Junior Stanislas and former Chelsea player Nathan Ake scored the goals to condemn the hosts to a loss at Stamford Bridge.
Swansea ended its losing streak in the Premier League with a 0-0 draw against Bournemouth on Saturday but failed to ease the pressure on head coach Paul Clement.
Arsene Wenger has called on Alexis Sanchez to deliver on the pitch and silence those Arsenal fans who jeered him.
Danny Welbeck's brace and an Alexandre Lacazette strike handed the Gunners some much-needed boost after their recent defeats.
Bournemouth were level on 62 minutes when they swept up field and Junior Stanislas polished off a fine move.
American owner Ellis Short doesn't mask the problems engulfing the club, saying "significant work" is now required to secure an instant return to the Premier League.
Bournemouth have been charged by the Football Association for a breach of its anti-doping regulations.