Etienne Capoue struck after just 32 seconds as Watford added to Leicester’s domestic woes by beating the Premier League champions 2-1 at Vicarage Road on Saturday.
Roberto Pereyra netted Watford’s second after 12 minutes and Riyad Mahrez’s penalty couldn’t revive Leicester.
Claudio Ranieri’s side are still looking for their first away win of the season and remain stuck within sight of the relegation zone.
Leicester will return to Champions League action against Club Brugge next week but while they have impressed in Europe, they continue to struggle for form back at home in the Premier League.
Once again Jamie Vardy failed to find the target, extending his club drought to 13 games although the forward did follow up his midweek strike for England by winning the penalty that allowed Mahrez to bring his side back into the game.
But the defensive weaknesses that have marked their disappointing title defence were again all too apparent as Watford claimed the victory that consolidated their place in the top half of the table.
Walter Mazzarri had been left incensed by Watford’s performance in the 6-1 defeat at Liverpool immediately before the international break and had insisted the anger shared by manager and players would ensure there would be no repeat.
But as anxious as the manager was to see his players recover quickly, their response was even more impressive than he might have hoped.
Just 32 seconds had elapsed when Watford exposed Leicester’s fragile defence to take the lead, and they had doubled that advantage within 12 minutes.
Pereyra was involved on both occasions, with the Argentinian’s left wing cross helped on by Troy Deeney’s backward header into the path of Capoue, who placed his volley beyond Leicester keeper Ron-Robert Zieler.
– Stunning opening –
The early strike clearly lifted the home side and Pereyra capped a stunning opening when he cut inside Danny Drinkwater on the left, moving the ball onto his right foot before curling an angled shot past Zieler from the edge of the penalty area.
Leicester needed to conjure a swift reply if they were to revive hopes of a first away league win of the season.
They were back in the game inside two minutes when Vardy was bundled over by Miguel Britos after collecting a pass from Shinji Okazaki inside the home penalty area.
Vardy’s lack of goalscoring form has been a major concern for Ranieri this season, but the timing of the run suggested the striker is nearing a return to the form of last season.
And when Mahrez converted the resulting penalty with an emphatic finish into the roof of the net, there was sense of relief among Ranieri’s side.
Leicester began to attack with more purpose but their defence – one of the side’s strengths during last season’s title triumph – struggled to get to grips with the threat posed by Watford.
Watford centre-back Younes Kaboul should have done better than direct a header over the bar from a corner midway through the first half.
And had Nordin Amrabat been able to collect Deeney’s pass when clear in front of Zieler’s goal, Mazzarri’s side would have reached the interval with a commanding lead.
Leicester approach at the start of the second period was much more convincing although the visitors’ attacking moves too often came to nothing because of a lack of quality service to Vardy.
And they were again almost caught out in the 65th minute when Zieler produced an outstanding reaction save to keep out Pereyra’s close-range header after Amrabat and Daryl Janmaat had combined to open up the Leicester left.
Leicester’s efforts became increasingly frantic as they searched for an equaliser but they remained unable to find the final pass that would have undone the resolute home defence.