Sharper of mind. And in movement. This is an entire new level. The demands of which many from Frank Lampard's starting XI have never had to meet. This isn't Bulgaria at Wembley. Nor even Wolves at Molineux. This is the real thing. The absolute pinnacle of the game. And even against an opposition in crisis and fighting amongst themselves, the demands from the first minute to the last are unlike anything this sport offers.
But as Lampard offered in the aftermath, there is much to be positive about for Chelsea.
Though defeat at home does put them on the back foot, Lampard can make a decent argument that Chelsea did deserve something from the game. They worked the visitors' goalkeeper, without truly stretching Jasper Cillessen. And to be fair to Ross Barkley, he did actually beat the Dutchman from the spot - only the crossbar managed to get in the way.
For Chelsea. For the neutral. A point would've been a fair result. But that's just it. At this level, what you get and what you deserve are two different things. And as the game wore on and as the hosts' defence creaked, it was becoming near inevitable that Chelsea would concede before Rodrigo Moreno's scruffy near post winner. Before then, Kevin Gameiro had sunk the entire Blues defence with one clever dash, only to blaze way over from a corner kick. Then moments later, Fikayo Tomori, who was excellent on debut at this level, played Valencia's attack onside, only for the final pass to be overhit. But the warning signs were there. For all of Chelsea's possession and their attacking moments, the focus was beginning to lapse. Chelsea's young players were beginning to fray at the edges. Those tiny details, the ones that mean so much at this level, were being ignored.
So, as mentioned, when Rodrigo found a way to beat Kepa Arrizabalaga at his near post, it really wasn't a surprise. Greater know-how. Greater experience. In the end, it was this that swung the balance. Rodrigo, a former Sam Allardyce protege no less, wheeling away in celebration, thumping the club's crest on his shirt...
Which, if he had had his way a fortnight ago, he'd have been doing in an Atletico Madrid shirt. The club's owner, Peter Lim, refusing to sell the wantaway striker in the middle of crisis talks with sports director Matheu Alemany. A week later, Salford City's co-owner would sack coach Marcelino and replace him with the man on the touchline last night, Albert Celades.
In other words, going into the game, it was carnage. Chelsea's opponents were in chaos. Nothing illustrating this better than Celades doing his pre-match presser on his tod. The players refused to send one of their own in to sit alongside Lim's appointment. Indeed, things are so bad that Anil Murthy, the VCF president, was pushed before kickoff if he had apologised to the dressing room for Lim's actions. His answer was to throw things back at the local press.
Inevitably, the best response came from the players. Led by skipper Dani Parejo in the middle of the park. Held together by Ezequiel Garay and Gabriel Paulista at the back. Those representing the VCF badge left London with their reputation intact. There's anger amongst the playing group of how their season has been undermined from within. But that wasn't allowed to creep it's way onto the Stamford Bridge pitch last night. Parejo, for one, made sure it wouldn't happen.
"The situation was not the best for us to go out to talk," he said at the final whistle, referring to the decision to blank the Celades conference. "I know that people may not understand why we did not go out, it was a very difficult situation for us and it was best to be silent, dedicate ourselves to playing and leave everything on the field."
Giving the support some insight on what's been said amongst the squad - and with a veiled dig at those upstairs - Parejo continued: "We are a family in there. This has been seen and we will show it because above all, at the club, we will pass through it, but the club will stay and we will give everything for the club because it is the most important thing."
For Chelsea, this was a night to live and learn. Tammy Abraham, just as he did at Swansea City and from the opening day at Old Trafford, will review and build from this. Much will be made from this low-key performance being played out in front of England assistant coach Steve Holland. But the idea that Holland, after all his years with Chelsea, could suddenly learn something new from watching Abraham last night is ridiculous. The lad will be called up and he will play for England. The Nigeria talk a lesson in astroturfing a story.
Abraham will learn from last night. From being buffeted by Gabriel. Being outpositioned by Garay. It was a setback, but a night he'll benefit from.
As will his teammates. After a couple of exciting weeks, they were hit by a brick wall in the form Valencia. On Tuesday, the reality of what is demanded by the Champions League bit down hard.