Jamie Vardy's record scoring streak ending was no problem for Leicester. Riyad Mahrez just grabbed a hat trick instead on Saturday and sent the season's surprise package back to the English Premier League summit, taking advantage of Manchester City losing.
Stoke tore City apart 2-0 at a chilly Britannia Stadium before Mahrez secured Leicester's 3-0 victory at struggling Swansea.
As City dropped to third, Arsenal went to second — two points behind Leicester — by halting a three-game winless run with a 3-1 victory over Sunderland that saw Olivier Giroud score for both teams.
Manchester United endured a fifth 0-0 draw in nine games in all competitions as West Ham frustrated Louis van Gaal's fourth-place team.
Tottenham missed an opportunity to go into the top four by drawing 1-1 at West Bromwich Albion.
Aston Villa gained only its second point since August by holding Southampton to 1-1, and Watford moved into the top half of the standings by beating Norwich 2-0.
Chelsea's title defense sunk to a new low on Saturday when Bournemouth became the first Premier League newcomers to beat the west London team in more than 14 years.
Bournemouth's 1-0 victory at Stamford Bridge will rank as one of the biggest in the 125-year history of the south coast team, which is playing in the top flight in the first time.
Having avoided defeat in its last two league games - encouraging results byChelsea's new modest standards this season - Chelsea's eighth loss in 15 league games will pile the pressure back on manager Jose Mourinho. Chelsea is approaching the midway point of the season an alarming 17 points behind surprise leader Leicester.
Having repelled waves of Chelsea attacks, Bournemouth's goal came in the 82nd minute when Glenn Murray exploited the hosts' failure to clear a corner by heading into the net less than two minutes after coming on as a substitute.
"The boys are gaining belief every week and I think it showed," Murray said.
A first league win since September took Bournemouth out of the relegation zone and was masterminded by manager Eddie Howe despite an ever-lengthening injury list.
"It's great to see for their own self-belief," Howe said. "If they can do it here they can do it anywhere."
"We've got the Special One," Bournemouth fans chanted about their 38-year-old manager, adopting Mourinho's self-styled description.
Mourinho's Chelsea is only two points ahead of Bournemouth in 14th place - in the league it won in May - following its first defeat against a newly promoted team since April 2001.
While Chelsea has enjoyed hundreds of millions of dollars of investment from billionaire Roman Abramovich in the last 12 years, Bournemouth has only benefited from more modest Russian investment from Maxim Demin since 2011.
Bournemouth came close to dropping out of the four professional leagues in 2009 before embarking on a remarkable rise. Chicago-based PEAK6 Investments last month bought a quarter of the team, which plays in a stadium with a capacity of less than 12,000.