Both qualified for the year-end tournament for the first time this year, Dimitrov after nearly a decade as a professional.

But the Bulgarian had looked completely at home, losing just one set in his three group matches and thrashing both finalist David Goffin and Rafael Nadal's replacement Pablo Carreno Busta for the loss of just four games in total.

Sock meanwhile lost his first match of the tournament, a straight-sets defeat to Roger Federer, before rallying wins over Marin Cilic and Alexander Zverev to seal his place in the last four.

These two have plenty of history, having faced off earlier this year at Indian Wells - Sock saved four match points before triumphing on home soil.

Dimitrov vs Sock RECAP

(* denotes next to serve)

10.20pm: Dimitrov is typically self-effacing and admits Sock really did trouble him.

“The last game took a lot out of me,” Dimitrov said.

“He’s an unbelievable player.

“That forehand gave me a lot of trouble.

“Today I didn’t play my best tennis but those are the days I like to win.”

He wouldn't mind a win in the final tomorrow either, here at 6pm. Join us then!

GRIGOR DIMITROV BEATS JACK SOCK 4-6, 6-0, 6-3!

Sock saves two match points from the baseline, one very much his work the other Dimitrov's fault, and when the Bulgarian nets a backhand, he hands his opponent a lifeline back into the match. However, Dimitrov plays the break point aggressively and saves it at the net.

And one point later he has a third match point, only to mis-hit a ball way over the baseline. That finishing line is such a tough obstacle! Dimitrov saves another break point when Sock's backhand finds the net. But at last, Sock nets on match point and the Bulgarian fans, of which there are hundreds if not thousands in here, celebrate wildly.

*Dimitrov 4-6, 6-0, 5-3 Sock

If you run around the forehand, it does leave the backhand down the line open, and Dimitrov has plundered it today. Another one brings up 15-30 but we find ourselves at deuce and Sock celebrates another free point with a big first serve. But his beautiful angled volley somehow clips the tape and stays on his side. Deuce again and Sock finds the worst possible moment to take his double-fault count to four.

But a spectacular forehand lands plumb on the line to save a massive break point...only for Sock to double-fault again! This time Sock is out-muscled from the baseline and Dimitrov will serve for the match.

Dimitrov 4-6, 6-0, 4-3 Sock*

Dimitrov returns the favour with a routine hold of serve. Tit for tat at the moment.

*Dimitrov 4-6, 6-0, 3-3 Sock

Easyjet has speedy boarding, Jack Sock has speedy holding. Back onto the Dimitrov serve in the space of around 90 seconds.

Dimitrov 4-6, 6-0, 3-2 Sock*

"Grigor, Grigor" they cry around the stadium as he curves another forehand into the open court.

What follows is a staggering point as the pair trade forehands, each more remarkable than the last, before Dimitrov drops a volley and Sock so nearly runs it down, ending up on his back while the crowd go wild. You can't fault his effort at the moment and it's providing fabulous entertainment.

*Dimitrov 4-6, 6-0, 2-2 Sock

There is a real edge to Jack Sock at the moment, as he closes out a hold to 15 with just his third ace.

Dimitrov 4-6, 6-0, 2-1 Sock*

There is little Sock can do about any of that. He attacks the net as well as anyone can, only for Dimitrov to pass him with the most remarkable of flicked backhands. A dead net cord follows and after a Dimitrov double-fault, the Bulgarian completes the hold.

*Dimitrov 4-6, 6-0, 1-1 Sock

Sock quietly but determinedly celebrates a couple of cheap points and holds to 15.

Dimitrov 4-6, 6-0, 1-0 Sock*

Sock doesn't necessarily look rejuvenated by that trip off court but he does seem a little mroe composed, containing his obvious frustration despite missing a backhand return off a second serve at 15-30, i.e. a real opportunity.

The chance does not pass though, as Dimitrov volleys long to bring up break point - which Sock squanders. The Bulgarian then finds a remarkable forehand winner that completely wrong-foots Sock and a poor backhand sees the game go.

He has blown that chance.

GRIGOR DIMITROV WINS THE SECOND SET 6-0!

A bagel in a semi-final would be most unsavoury but that is exactly what we've got here, Sock netting a weak double-handed backhand. 70 minutes gone and we're going to a decider.

Dimitrov made 12 unforced errors in the opening set. That one saw him produce just four. Sock goes off court for a comfort break, but no coincidence that it comes just after a chastening few minutes.

Dimitrov 4-6, 5-0 Sock*

There is still some life left in Sock, as he proves with a very special forehand return winner. But Dimitrov is starting to find his range and fires a terrific forehand past Sock to seal the game.

*Dimitrov 4-6, 4-0 Sock

Oh dear. Sock has gone to pieces here, to the delight of the tens of Bulgarian flag-wavers in the crowd. Dimtrov brings up two break points and only needs one. Wonder if Sock might just conserve energy for the deciider at this point.

Dimitrov 4-6, 3-0 Sock*

Well, just as it was in the first set, it's 3-0 Dimitrov. And we all saw how that ended.

*Dimitrov 4-6, 2-0 Sock

A couple of points lost at the net and Sock finds himself break point down, loops a backhand both wide and long and inexplicably challenges. Overly desperate that from a man up by a set.

Dimitrov 4-6, 1-0 Sock*

A comfortable hold for Dimitrov, who will need to get his serving percentages up if he is to get back in this match.

JACK SOCK WINS THE FIRST SET 6-4!

Oh referee! Sock plays a forehand pass, after running down the drop shot, so sublime it seems unfair. It followed a double-fault though so no lack of variety.

A poor missed volley from Dimitrov hands Sock two set points, the first of which he converts! Absolute scenes. Maybe it's Jack Sock's world and we're all living in it.

Dimitrov 4-5 Sock*

Superb, aggressive tennis from Sock, slapping a forehand winner off the Dimitrov second serve to claim 15-30, but then slaps his racket in frustration after netting a backhand.

However, break point does follow, only for Dimitrov to do the job off the first serve. But a fourth double-fault of the set gives him another opportunity and Dimitrov chips it long. That's five of the last six for the American.

*Dimitrov 4-4 Sock

Probably Sock's best hold of the match, including a sumptuous half-volley during a net exchange that just lands inside the baseline. Lovely tough.

Dimitrov 4-3 Sock*

More good serving from Dimitrov, who will use that weapon to great effect, but will also wobble on second. He shows that with a double-fault into the net at 40-30 and another one straight afterwards!

He gets himself out of trouble but that was a big wobble.

*Dimitrov 3-3 Sock

Far from perfect from Sock, who very nearly double-faults at 30-15 and flays a framed forehand about 40 feet beyond the baseline - but he still holds to restore parity.

Dimitrov 3-2 Sock*

Dimitrov leaks a couple of forehands and an excellent forehand return gives Sock a break-back point - which he promptly converts by skipping round a couple to unleash that forehand once again. Not a clean winner but the power is too much for Dimitrov, who can only find the net. 

*Dimitrov 3-1 Sock

Sock is a bit all over the shop here, pushing a short ball long when Dimitrov fakes to cover the drop shot and puts him off. He does at least save the break point and finds his two aces of the match to get him out of the game. Sock on the board.

Dimitrov 3-0 Sock*

The players sit down for the first time and Sock is yet to get on the board. Dimitrov remember has destroyed his last two opponents for the loss of just four games. No-one wants to see another one of those matches though. Not in semi-final.

*Dimitrov 2-0 Sock

Sock will have to play at a high level to win this match, and two more unforced errors in his opening service game put him under pressure at 15-30. He double-faults by a mile before hitting his first winner of the match to save the first break point.

But the Bulgarian canters to the net at 30-40 to put away a floaty, sliced bachand - to the delight of a crowd thick with fellow Bulgarians it would appear!

Dimitrov 1-0 Sock*

I'm likely to talk about Sock's forehand a lot today - but it is exciting. Short, fluid backlift and untold power. There is a sharp intake of breath in the stadium almost every time he hits it. A return at 40-15 is particularly emphatic

Dimitrov is pretty handy from the baseline too though and reminds us as much with a couple of booming forehands. Sock takes him to deuce but he holds nevertheless. 

8pm: Ball kids? Check. Line judges? Check. Chair umpire? Check. Offensively loud music? Oh but of course.

One thing we are missing is a couple of chaps with rackets. They are incoming though: Jack Sock all quiff and teeth while Grigor Dimitrov is dark, stormy and has eyes you could get lost in. That thousand-yard stare is something else.

Where's your money? I'm going Dimitrov but those around me are arguing it will be closer than I think. Opinion is divided you might say.

7.40pm: David Goffin awaits the winner of this match, meaning we will have an all-debutant final no matter what.

Dimitrov has been imperious all week but can the powerful Sock break his rhythm? He leads the head-to-head 3-1 and is not the Bulgarian's ideal opponent. That said, Dimitrov is playing some of his best tennis at the moment and looked unstoppable in the group stages.

They'll be on court in just about 20 minutes.