The key question is whether Brentford have had their moment - but their assurance, and Chelsea's ongoing anxiety, means the answer to that remains very much undecided.
The reason the FA Cup retains such intrigue, if not quite its old prestige, is because of the way individual moments have shaped its history. Any time we see the kind of upset that Brentford came so close to securing in an engaging game at Griffin Park, the players involved speak of the individual instances that made them just know the dynamic was different; the times when the game seemed to turn and everything was up for grabs.
Afterwards, Brentford's players were talking about their disappointment at not going through. That's how vulnerable Chelsea were, and how vigorous - and how impressive - the Bees were.
The feeling may be that Brentford have lost their chance, but you'd have thought exactly the same after Oscar's equaliser early in the second half. When a Premier League side gets back on terms with a lower division side, they often go on to power through. Brentford manager Uwe Rosler admitted he had thought that was going to be the case but his team re-energised, released Tom Adeyemi and won the penalty from which Harry Forrester reclaimed the lead.
It was a hugely impressive recovery in terms of character and courage, even more praiseworthy than the manner in which Brentford started the game. And that's saying something.
With the industry and intensity of midfielder Jonathan Douglas setting a fierce pace, and the quality of the likes of Manchester City academy graduate Shaleum Logan showing through, the League One side dominated the first half.
The manner in which Douglas chased down a loose backpass in the opening minutes and forced Ross Turnbull into a wayward kick-out laid down a marker. Chelsea were persistently pressured into errors, with their goalkeeper often the most culpable. After an indirect free-kick from a backpass was fired just over and Adam Forshaw struck inches wide, there was a feeling of inevitability when Turnbull parried a Forrester shot into the path of Marcello Trotta, who gave Brentford a deserved lead.
Things were blowing their way, with Rosler reflecting: "We played the first half with the wind. That was a very good decision. We wanted to hang in. We wanted to stop the ball between the lines."
That was certainly the case and, as Chelsea struggled against such concerted and concentrated effort, Rafa Benitez all but conceded they had been complacent and not ready to match Brentford's level of effort.
"In the first half, we didn't do what we had to do," he said. "We knew it would be difficult. We made too many mistakes in the approach of the game, the way we wanted to play. We knew they would be high-tempo, pressing."
The opening period led many Chelsea fans to chant that Benitez didn't know what he was doing. But when that was mentioned to the Spaniard, he said the successful introduction of Juan Mata meant he could "guarantee we know what we are doing".
It cannot be denied that the No. 10 - who has undoubtedly been Chelsea's player of the season so far - altered the dynamic of the tie. The Premier League side finally started to control the game in the manner Benitez so often preaches about, but that Chelsea hadn't managed at all.
It showed that all the energy, pressing and intensity a team can muster can't quite match superior talent when it's properly applied, something also illustrated by Oscar's superb equaliser from Mata's cross.
And it seemed that Chelsea were only going to keep hammering home the point further when, a few minutes later, the two creators combined again and their nimble footwork enabled them to inventively evade some fierce challenges.
Given that Brentford were beginning to look jaded and Chelsea were finding more and more openings, it was surprising that Benitez didn't bring on Demba Ba to stretch the home side, but he argued that was "because the team was doing well".
But he was forced to bring the striker on after Adeyemi broke into the area and tumbled over Turnbull, with Forrester restoring Brentford's advantage.
The change had an instant effect, but perhaps not in the manner intended. The forward that many fans now want Ba to play instead of, rather than alongside, was galvanised into one of his finest strikes for Chelsea. Given the problems that have afflicted Fernando Torres for two years, it is easy to joke that him producing a truly telling strike is the greatest upset of all. But the finish with which he made it 2-2 was certainly a bit of magic.
It might have become really disenchanting for Brentford, though, had a late penalty for handball been given. Instead, the complaints were waved away - perhaps rather surprising given how these things usually go.
That, however, was the story of the day. Rosler spoke of how the "football God" was with his team and that they had "deserved that luck", but stressed that they had "earned the right to play at Stamford Bridge".
That was undeniable and, given Chelsea's issues at home, there is every chance Brentford, with their admirable approach, can seize the moment again.
Benitez, meanwhile, is suffering a few too many moments like this.
Be part of the Budweiser 2012-13 FA Cup fan film. Share your photos on Twitter: #tothedream