Only time will tell how memorable this season will be for Everton.
If the worst comes to pass and the Blues get relegated it will go down as one of the most catastrophic in the club's history. No-one associated with the club will forget it.
If Frank Lampard's men pull themselves to safety then, in years to come, it may well blend into the wider period of frustration that has characterised the early stages of Farhad Moshiri's reign.
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What will not be forgotten, however, is the way Everton supporters rallied around their club in its hour of need. Never has this been clearer than today.
And rarely has the impact of that support been so clear than it was in helping those on the pitch secure this monumental victory against the reigning European champions.
The gut-wrenching, hope-sapping comeback by Burnley on Saturday could have winded a fanbase called upon to back the players. It was deflating result and threatened to undermine efforts to mass a show of unity and hope amid the pressure of a relegation battle in which momentum was building in the wrong direction.
But Everton is no ordinary club and its supporters are the foundation of its greatness.
Thousands answered the call of fan groups, including the Everton Fans' Forum, to line the tight streets surrounding Goodison Park to welcome the players' coach. So significant was the size of the crowd the arrival of the bus was delayed by 30 minutes. The blue air fizzed and crackled with the noise of terrace chants and the burn of smoke bombs.
This intensity was matched inside Goodison Park as the players walked onto the hallowed turf to a sea of blue and, as requested by the supporter groups, a cauldron of noise.
Everton launched into a lightening start in an electric atmosphere, Anthony Gordon winning a free-kick in the opening seconds that he then struck over. The following 45 minutes ebbed and flowed. The burst of excitement calmed, Everton never looked in real danger though they struggled to carve out opportunities for themselves.
The result was a first-half of stunted attacks and a little needle as several players earned yellow cards in a game neither side could grasp control of.
As the home supporters dispersed into the concourses the mood was confused. What would a draw mean? It would be a valuable point closer to Burnley and Leeds United but would also take Everton's destiny out of the club's control, leaving the gap at four points with the Blues left with just one game in hand on both.
Assessing the true value of a point was rendered meaningless in the following 45 minutes. One of the biggest 45 minutes, potentially, in Everton's Premier League history. One of the biggest in Lampard's managerial career too.
Those 45 minutes largely boiled down to the events of the first 600 seconds, a microcosm of a season in which two Blues heroes added another chapter to their Goodison Park stories. First it was Richarlison. The Brazilian, who has tried so hard to lift his teammates in recent weeks - scoring twice at Burnley and, so memorably, in the last minute at home to Leicester City - provided a goal that will live long in the memories of those in the ground.
If you could have bottled the intensity and passion displayed outside the stadium before kick-off and recreated it on the pitch, you would have had the first five minutes of this second half from Everton.
Its highlight was the sight of Demarai Gray and Richarlison hunting down Cesar Azpilicueta on the edge of his box, stealing the ball and leaving Richarlison to slot home coolly in front of the Gwladys Street stand that would have sent its roof into orbit had the structure not been built to last.
Before the celebrations had died down Everton went on the collective hunt in Chelsea's final third again, forcing the ball into the path of Abdoulaye Doucoure who squeezed in Vitalii Mykolenko. His shot was wild and wide as he flayed an opportunity to score his first goal as a Blue.
The action then turned to the other end. When the players had stepped onto the pitch at 2pm the Gwladys Street unfurled a giant banner declaring Jordan Pickford England's number one.
Across a 90 second spell in the aftermath of Richarlison's goal he produced two stunning saves to back up that statement. First, Mason Mount struck both posts, Everton getting an uncharacteristic slice of luck in what has been a season of misfortune. It was short-lived as the ball fell to Azpilicueta with the entire goal to aim for. Out of nowhere, off balance, the scrambling Pickford recovered to pull off a seemingly impossible stop. Seconds later he was called into action again as Antonio Rudiger, free at the back post and just yards out, fired on target. With hope seemingly lost Pickford threw himself at the ball, stopping another certain goal, this time with his face.
The last 15 minutes - which became 22 when seven were added on to the shock and dismay of the home bench - were a sickening, chaotic free-for-all in which Chelsea largely controlled the ball as they probed at Everton's defensive lines but in which the home side repeatedly threatened on the counter-attack. Gray curled just over from 20 yards, Salomon Rondon almost connected with a cross at the end of a move he had started by outmuscling Ruben Loftus-Cheek on the halfway line, and Gordon forced a low, near-post save from Edouard Mendy.
Three weeks ago Everton saw out a 1-0 win over Manchester United at Goodison Park in which Pickford made one late, sensational save but which was otherwise negotiated with relative comfort. That was not the case today. This was backs-to-the-wall. This was a rear-guard action that needed all that passion, intensity and dedication displayed so fervently by the Everton supporters.
The club's players have relied heavily on their fans in recent weeks, on Goodison Park being the weapon that helps fire them to safety. When the club called on them once again, they rallied without reservation. Against Chelsea, the players responded with a performance to match. Because of that, Everton's fate is still in their own hands.
If safety is ultimately secured then, as the years go by, this may well be seen - on the pitch - as a disappointing but unremarkable season that fades in the memory of most supporters.
Few involved will quickly forget what happened off it on Sunday though, as this special fanbase united for the boys in Blue, who responded in the best way possible.
