Djokovic 4-6 6-7 Alcaraz
Game and the second set to Alcaraz.
The Spaniard has doubled his lead. He wins the tie-break by seven points to four.
In point seven, Djokovic charged up to the net and managed to read the Alcaraz drop shot.
You could feel the effort from both players. The crowd loved that moment.
Alcaraz, who fist-bumped towards the fans, has just been sharper and fresher in the key moments.
Point 10 was a 131mph serve bomb. One of his biggest serves.
Point 11 was a second-serve at 100mph but the Djokovic return was long.
Djokovic has come from two sets down on eight occasions but at 38, against the impressive Alcaraz, who is 22 years old, it would be a herculean task to do so here.
The odds are greatly against him.
Are we witnessing the end of Djokovic at the US Open? He might only have one more set to go.
Djokovic 4-6 6-6 Alcaraz (tie-break)
It is the first changeover of the second-set tie-break, which happens after six points.
Alcaraz has the advantage. He leads 4-2.
The first person to seven points, albeit with a two-point advantage, will take the set.
Djokovic smiled when he won the third point, stretching superbly to the drop shot with a lob and then Alcaraz could not control his backhand smash.
That rally was 18 shots in total.
But a later drop shot from Djokovic is too short. He is struggling here. He is in deep trouble.
Djokovic 4-6 6-6 Alcaraz
Alcaraz is in a good serve rhythm and forces the tie-break, dropping just one point in game 12 of set two.
An 128mph ace down the centre in point three was very impressive.
Djokovic has asked the umpire to call the trainer, who is waiting in the wings.
Suspicions about his fitness are confirmed. He has an issue. We will find out soon what that is.
But it will be after the tie-break. By then he could be 2-0 sets down.
It could be the foot blister, the neck, the back, the elbow.
Djokovic 4-6 6-5 *Alcaraz
One more game and we will see a tie-break.
Djokovic does his part with a routine hold.
Alcaraz is now serving to stay in the second set and keep his advantage.
This could go either way now.
The crowd has tried again to lift the spirit of Djokovic.
Both players have had two days off since their quarter-final wins.
How fresh they will be, how much energy they have in their legs, will be tested here.
Djokovic* 4-6 5-5 Alcaraz
Alcaraz holds his serve and does not give Djokovic much of a sniff.
We are level in this set.
We might be heading to a tiebreak at this rate.
Alcaraz is playing in the semi-final of a major for the first time without dropping a set en route.
That fautless record this fortnight will be tested over the next 10 minutes.
More than 90 minutes have passed in this contest.
Djokovic 4-6 5-4 *Alcaraz
Game nine opens up with a double fault from Djokovic. That is the second one he has produced in 19 games.
Point three was a 27-ball rally, the longest so far, and it ended when a backhand from Alcaraz bounced off the net and on to his side of the court.
It is the most physical rally we have seen. That is more what we want to see.
Djokovic was lucky there. He won’t want too many of those long exchanges.
Yet from love-30 down, Djokovic won the next four points to hold serve.
Alcaraz kicked his towel bucket in a moment of frustration. He has produced 25 unforced errors to Djokovic’s 17.
