Fast-starting Watford inflicted Premier League champions Leicester's sixth defeat of the season with a 2-1 win at Vicarage Road.
Etienne Capoue scored after 33 seconds and Roberto Pereyra's fine strike after 13 minutes doubled the advantage.
Jamie Vardy was felled for a penalty converted by Riyad Mahrez two minutes later, but the Foxes never really looked like finding an equaliser as Watford responded from the 6-1 loss at Liverpool.
Leicester still have more points than Chelsea, their predecessors as champions, did at the same stage last season. The Blues had 11 after 12 games, but are too close to the drop zone for Claudio Ranieri's liking.