Chelsea just about maintain sufficient energy to remain standing; Manchester United continue to slightly stumble. In that, as much as this replay took on a significance beyond even the competition and individual fixture itself, its result was more a consequence of everything happening around it.
For United, the almost mechanical rhythm developed to build and maintain an emphatic but hardly empowering lead in the title race seems to have sapped them of the spark required for contests such as this. Sir Alex Ferguson later stated they "lacked the composure to win the game", but as much of an issue was the vigour. As the United manager himself admitted, he "couldn't really see" his team scoring.
Most tellingly, we didn't get the typical United late siege evident against Real Madrid in the Champions League or even against West Ham United earlier in this competition. Most obviously, Robin van Persie has lost the ruthlessness and rampant form.
Chelsea, meanwhile, almost have the opposite issue. They must maintain a sufficient edge in every game given the stark consequences of any defeat or dropped points. And, as flawed and frustrating as Rafa Benitez's rotation-based approach can be, this game almost offered a qualified justification. Indeed, it almost summed it up.
Because, across this tie, Chelsea were undeniably as wasteful as they've often been in the league - even as regards having to play this replay in the first place. Just as Juan Mata was denied an opportunity in stoppage time of the match at Old Trafford, Eden Hazard missed a chance to kill it long before the end here.
Ultimately, Chelsea just about displayed the efficiency to put them through - and, it must be said, in the most effervescent manner.
Mata and Demba Ba offered one of the moves of the season; Petr Cech provided one of the saves of the season. In truth, they were moments of exquisite quality which greatly elevated a mostly drab game. Far more characteristic of the contest was the sloppiness of touch and finish displayed throughout.
The easy explanation is that they both played less than 48 hours beforehand in the Premier League. That, however, did seem to be offset by the fact that only seven outfield players actually started both of the clubs' respective games and that energy didn't initially seem to be the problem. By contrast, there was a lot of rushing about with no end result.
Ashley Cole's hamstring injury almost summed up the first half: the two sides cancelling each other with speed but no specific application. At the same time, it can't be overlooked that it was the two Chelsea attackers rested during the 2-1 defeat to Southampton that ultimately decided the game.
Displaying the mental sharpness absent in so many others on the pitch, Mata paused and picked out a glorious lofted ball. Ba gave the United defence the slip to display expert control of finish.
Ferguson's side could do no such thing. Devoid of the dynamism that has marked so many games this season, as well as the opening 20 minutes of the first game of this quarter-final, they were forced to introduce Van Persie. Unfortunately for United, it was not the Van Persie of August to January.
Offered two chances, the forward squandered them both. And, even if the first was more difficult than it looked given the height and speed with which it was delivered, a player of his quality should still have finished.
It would be difficult to be too critical of Van Persie given that a drop-off at some point was always going to be inevitable and that it was his goals which directly put United into such a commanding league lead in the first place. At the same time, it might be that very lead which has ironically caused both he and his team to slacken off.
Similarly, there is the unfortunate reality that the Dutch player provided the goals that will deliver the title, but missed the key chances that cost them in both the Champions League and FA Cup.
In winning a 20th title, he has helped them make history, but it will not feel as historic a campaign as it might have done.
Benitez, however, now believes this could yet be a "great season" for Chelsea. It must be said they did show admirable grit to keep that prospect alive. As much as Van Persie eventually got free for both those chances, one of the reasons those opportunities felt so relevant was because they were so rare. Chelsea fought for every inch of space and, in the tense closing stages, admirably realised the importance of getting a touch for a throw-in rather than allowing United another opportunity for an opening.
In a contest and run-in in which energy is seemingly at a premium, it was just about enough. It does not mean that Chelsea will ultimately meet all their targets. But, for the moment, they remain on track.
United are out of the FA Cup and seemingly running out of steam. Chelsea are in the semi-finals and, still, just about keeping things in check.