Perfect day for Osman
Everton midfielder Leon Osman picked the perfect way to mark his 400th appearance for the club as his first league goal since March ended high-flying West Ham's five-match unbeaten run.
The 33-year-old, who in reaching the landmark joined an elite group of a dozen others led by the great Neville Southall, capped a controlled and creative performance with the winner 17 minutes from time.
His intervention prevented his side from squandering another lead this season after substitute Mauro Zarate cancelled out Romelu Lukaku's controversial goal.
West Ham, who began the day in fourth place, loudly and correctly complained the first-half opener was offside and although it was allowed to stand the Toffees would have dropped another two points had it not been for Osman's late contribution.
Everton's resources in midfield were limited with Gareth Barry and Darron Gibson sidelined by injury but Osman calmly held the central ground with James McCarthy, who showed no ill-effects from the hamstring injury which kept him out of the Republic of Ireland's recent matches and provoked stinging criticism from assistant manager Roy Keane.
West Ham, like their hosts significantly depleted by injuries and were crucially missing the attacking influence of Stewart Downing, Enner Valencia and Diafra Sakho, massed their defence with five across the back in an attempt to deny any width.
Roberto Martinez attempted to counter that by deploying Kevin Mirallas, on his first appearance since September 27 after a hamstring injury, as an out-and-out winger to stretch play but that just meant there was even less room for full-back Seamus Coleman to charge into in characteristic fashion.
The first time he did get forward, picked out by a brilliant Osman through-ball, his cut-back presented Steven Naismith with a good chance which he ballooned over.
Osman then put Naismith in with a helpful rebound off a defender but the Scotland international's shot was from such a narrow angle that when it went through the legs of goalkeeper Adrian the ball continued on a path away from goal.
Barkley, who incurred the fury of Hammers captain Kevin Nolan with a blatant dive to win a free-kick, had a hand in the opening goal but not as much as the assistant referee who failed to spot Lukaku was in an offside position from the initial shot.
Via the aid of deflections off James Tomkins and Winston Reid the ball dropped to the Belgium international who rammed home his 21st goal in 50 appearances for the club.
Everton have not been entirely comfortable going ahead this season and Sylvain Distin almost contrived to present Morgan Amalfitano with an equaliser trying to pass out of defence but the Frenchman fired wide.
Even though Lukaku had the ball in the net again from a quick counter-attack, ruled out because both he and Barkley from whom he nicked the ball off were offside, there was a growing sense that Everton had lost control.
That was confirmed when McCarthy's over-the-top tackle to take the ball and ankle of Amalfitano sparked a melee with almost every member of the West Ham team looking to confront the Republic of Ireland midfielder resulting in he and initial aggressor Reid being booked.
In his first start of the season West Ham striker Andy Carroll's most significant contribution in the first half had been a perfectly-placed raking crossfield ball to pick out full-back Carl Jenkinson whose cross was hacked clear by Phil Jagielka.
However, the introduction of Zarate in the 51st minute produced an instant impact as four minutes after coming on he weaved his way to the edge of the penalty area and unleashed a shot which took a looping deflection off Jagielka and over Howard.
McCarthy responded with a shot from distance which flew just over the crossbar while Amalfitano had low shot tipped wide by Howard.
The decisive moment came in the 73rd minute when, having blundered for the opening goal, the officials got it spot on as referee Mark Clattenburg played a good advantage when Collins brought down Lukaku and substitute Samuel Eto'o crossed for Osman to turn the ball home at the far post.
Even then it required an instinctive reaction save with his leg by Howard to deny Collins.