Everton threw away two valuable points at Goodison Park as Olivier Giroud scored a last-minute header to hand Arsenal a dramatic 2-2 draw on Merseyside.
Roberto Martinez's side looked to be coasting to an easy 2-0 win thanks to goals from Seamus Coleman and Steven Naismith, but their defence crumbled in the dying minutes to gift the Gunners a point.
First, Aaron Ramsey bundled home a Santi Cazorla cross and then, with 30 seconds to go, Giroud headed past Tim Howard thanks to some sloppy marking from Sylvain Distin.
It was a cruel blow to Everton, who really should have secured an early blow over their rivals in the hunt for Champions League qualification.
The Toffees were far more clinical and efficient in front of goal right up to the point where Ramsey found the net in the 83rd minute.
In fact, Arsenal looked blunt and impotent in the final third for most of the match.
Alexis Sanchez started as a lone frontman, but, despite his trickery and pace, he never troubled Phil Jagielka and Distin - who have a combined age of 68 - and he was hooked off at half-time.
His replacement Giroud fared just as poorly straight after his introduction, wasting a couple of good chances.
But the France striker came up with the goods in the final minute to send Everton home fans wondering how on earth they did not win.
Arsenal had the better of the opening 15 minutes, but it quickly became apparent they were lacking a clinical edge.
Ramsey tried to carve open the home defence with a series of cutting passes, and there were plenty of fancy touches from Sanchez, who harassed the home defence with his pace.
But Howard remained untested in the Everton goal.
The only chance Arsenal mustered in the first half came when Coleman cleared straight to Alex Oxlade-Chamberlain. Luckily for the hosts, the England winger side-footed wide.
It took just a couple of minutes for Coleman to get back into Martinez's good books.
The Republic of Ireland full-back climbed high at the back post to nod Gareth Barry's delicate chip past Wojciech Szczesny and give Everton the lead.
Romelu Lukaku played a part in the goal, selflessly ducking to give Coleman a clear header, and Mesut Ozil gave Everton a helping hand with some sloppy marking.
Arsenal were rattled, and they almost went 2-0 down moments later.
Naismith looped a header over Calum Chambers and straight into the path of Kevin Mirallas, but his shot trickled inches wide.
Chambers then carelessly clattered into Mirallas, giving Everton a free-kick on the edge of the box.
Mirallas bent the resulting free-kick up and over the wall, and the Everton fans rose to their feet thinking the Belgian had scored, but the ball had instead rippled the side-netting.
Arsenal manager Arsene Wenger vented his anger at referee Kevin Friend for booking Per Mertesacker after a foul on Naismith.
And the Frenchman's mood darkened just before the break when Everton doubled their lead.
Lukaku shrugged off Mertesacker inside the Everton half and hurdled the sliding challenge of Chambers before sprinting at the Arsenal defence on the break. The Belgian cleverly cut inside from the right flank and flicked the ball through to Naismith, who beat Szczesny from close range.
It was a beautiful goal, but one that should have been ruled our for offside, replays showed.
Wenger had seen enough of Sanchez and replaced him with Giroud at half-time.
Arsenal's misery continued, though as Giroud managed to blast a volley over from close range just 58 seconds after his introduction.
Jack Wilshere was lucky to escape with a yellow card for a late sliding challenge on Barry. Mathieu Debuchy followed him into the book with a petty challenge on Naismith.
Arsenal dominated possession, but they still did not look like scoring.
Howard made his first save of the match in the 68th minute from Giroud, who rolled a weak shot into the American's hands from 12 yards.
Wenger looked to inject some life into his side by replacing Wilshere and Oxlade-Chamberlain with Cazorla and Joel Campbell.
Arsenal finally found the net with seven minutes to go.
Cazorla flashed a low ball across the box in front of six Everton players, and Ramsey prodded home.
A cagey atmosphere descended upon Goodison Park, and the home fans breathed a huge sigh of relief as Giroud wasted a good chance to level with a free header.
The Frenchman had the last laugh, though, stunning the home crowd into silence with a last-minute header from Nacho Monreal's cross.