There was a point in the third set of today's men's semi-final between Roger Federer and Novak Djokovic when I knew that Fed was going to win.
I don't remember exactly what the score was but I think they were even in games and even in sets and battling it out with long rallies and miraculous shots. Djokovic managed to get to a deep Federer forehand, but barely, and his high, arcing return set Roger up for an overhead smash.
In the past, I've seen Federer hit these kinds of overheads somewhat gently, content to collect the point and move on. Not this time. Against Djokovic in the pivotal third set of the 2012 Wimbledon men's semi-final, Fed absolutely hammered the overhead smash, his face a mask of barely controlled fury.
His concentration was complete. His focus unshakable. His determination evident.
It was an image of Roger Federer that I haven't seen in a long time.
And then I knew. Whatever concerns I've expressed in the past about Federer having lost his edge now that he's set all the records, collected all the money, garnered international fame and cemented his place in the history of tennis all disappeared in that single moment.
For this tournament at least, the Roger Federer of 2005-2012 is back in full force.
I almost want to type that Novak Djokovic didn't stand a chance against this version of Roger Federer but that's not fair to the world number one. Djokovic stands a chance every time he steps onto the court, no matter who he faces, no matter how focused his opponent might be.
But, on this day, against this rejuvenated Federer, Djoko would have to bring his very, very best to win. And, as it turned out, he just couldn't do it.
So now it's Andy Murray's turn to measure himself against a towering Roger Federer, who appears to be, for the moment at least, back on top of his game.
Both Murray and Federer will take to the Wimbledon court on Sunday aiming to make a little history. Both will be supremely motivated and, despite the fact that this is basically a home game for Murray, I suspect the Centre Court crowd will be strongly divided in their loyalties.
If Roger plays with the same focus and determination on Sunday that he displayed today, I don't think Murray stands a chance, no matter how motivated he might be.
The 2012 men's title at Wimbledon rests on the racket of Roger Federer.