Leicester's improbable march towards a first Premier League title continued at Crystal Palace overnight as Riyad Mahrez scored a winner that put them eight points clear at the top.
Algerian Mahrez, one of the outstanding contenders for English football's player of the year, latched on to Jamie Vardy's 34th-minute cross to net his 16th league goal of the season.
Shinji Okazaki spurned a couple of chances early in the second half as the leaders attempted to ram home their advantage and Leicester, under severe pressure near the end, almost paid the price when Damian Delaney hit the bar in the dying seconds.
The defeat continued Palace's slide down the table after 13 league games without a victory and they remain the only team in the top four divisions of English football to have failed to have won a league game this year.
Meanwhile Stoke stayed in the hunt for a Europa League spot with victory against a lacklustre Watford.
Jon Walters put the visitors ahead, finishing off a 13-pass move from close range, and Marko Arnautovic was unlucky to have his effort ruled out for offside as Stoke dominated.
Joselu slotted Stoke's second six minutes after the break after Walters had returned a weak clearance by Watford keeper Heurelho Gomes into the path of the Spaniard.
Troy Deeney scored a late consolation for the home side who are virtually assured of staying up.
In Arsenal's game, first-half goals by Danny Welbeck and Alex Iwobi earned the Gunners a first win in four league games to revive their title hopes in the early kickoff at Goodison Park.
Welbeck was denied by the woodwork in a lively opening before Alexis Sanchez's defence-splitting pass played him in to round keeper Joel Robles and score after seven minutes.
Arsenal, who began the day 11 points behind leaders Leicester City with a game in hand, were slick in attack and doubled their lead after 42 minutes when Iwobi, in his first league start, raced through to beat Robles with a cool finish.
FA Cup semi-finalists Everton struggled to create much in the way of clear chances and could have lost by more against an impressive Arsenal side who stayed in third place.
At Stamford Bridge, West Ham's charge towards a Champions League spot was halted by a late Cesc Fabregas penalty as Chelsea remained unbeaten in the Premier League under interim manager Guus Hiddink.
Slaven Bilic's side were good value for their lead but Fabregas, whose free-kick had drawn Chelsea level on the stroke of halftime, converted after Ruben Loftus-Cheek had been brought down by Michail Antonio.
Manuel Lanzini gave West Ham the lead in the 17th minute, tricking Branislav Ivanovic before curling a superb shot into the top corner and Andy Carroll restored their lead on the hour.
Carroll had been on the pitch only a couple of minutes when his scuffed shot embarrassed Chelsea keeper Thibaut Courtois.
Norwich City earned their first win in 11 Premier League matches with a Robbie Brady goal that could prove critical in the battle against relegation.
The Irish international scored with the undistinguished game's first shot on target five minutes after halftime as the Canaries put three points between themselves and the trio in the relegation zone.
West Bromwich Albion's Stephane Sessegnon spurned the best opportunity of a dismal first half, homing in on goal but screwing his shot woefully wide after Gary O'Neil had given the ball away.
The Baggies were left ruefully reflecting on their first home defeat in seven league games while Alex Neil's men could celebrate their first victory after six successive away defeats.
Reuters