Guus Hiddink's Chelsea produced a clinical display to beat Arsenal 1-0 and revatilise their league campaign. For Arsene Wenger, it was always going to be a tough job once Per Mertesacker was sent off, as early as the 18th minute.
Koscielny stabbed home a flick-on from France team-mate Olivier Giroud in the 72nd minute at a rain-lashed Emirates Stadium and Leicester were held 0-0 by Bournemouth, with Riyad Mahrez squandering a penalty.
Arsenal manager Arsene Wenger found himself attacked from all sides on Wednesday after his selection decisions backfired to leave his team facing an embarrassing group-stage exit in the Champions League.
Chelsea remain high on confidence despite their poor start to the season, and if anything the current struggles has made the players stronger, goalkeeper Asmir Begovic said ahead of Wednesday`s Champions League game at home to Maccabi Tel Aviv.
After an error-strewn league debut Petr Cech provided a timely reminder of his undoubted class with some stunning saves as he marshalled a nervous Arsenal to a goalless draw against Liverpool on Monday.
Premier League 2015-16 gameweek 2, Sunday football witnessed Arsenal winning their first game, beating Crystal Palace 2-1 in a London derby, then reigning champions Chelsea thrashed by Manchester City 3-0 at Etihad Stadium.