Dominic Thiem is fully charged after that dip in the second set. A 93mph winner moves him 40-0 ahead and then hits a first serve out.

Surprisingly he grabs another ball quick sharp and shapes up for another wallop... net. That's a double fault. He thought the first one was called a let and went for another first serve. Ooops.

No major bother though as he wraps up another strong hold.

Bubbling along nicely isn't it? Both players are leaving it all out there in what they know is their final match of a long year.

Now then Stefanos, how's your mettle? Suddenly the tables have turned a touch.

Thiem nailing another forehand for 15-15 before Tsitsipas regains control with an aggressive backhand winner.

The Greek steps in again, forcing Thiem to skew a return wide into the tramlines for 40-15.

Tsitsipas can't control a crosscourt forehand, perhaps struggling to adjust to the increased power from Thiem, then settles into the next point nicely to wallop a forehand winner for the game.

(And yes, I know Stan Wawrinka is still the OHB GOAT.)

Dominic Thiem reiterates his claim for the best single-handed backhand in the game with a crisp winner down the line that Tsitsipas doesn't even bother going for. That's 30-0.

Thiem continues to hit hard and moves within a point of the game, another crunching forehand from just inside the baseline sealing it.

Guess who's back!

Boris Becker
Three-time Wimbledon champion on BBC TV

Thiem looks like his back in the zone, his facial expression is very focused.

We know how good Tsitsipas is in these pressure moments on his serve and again he saves the first break point.

But Thiem makes the most of his second opportunity when Tsitsipas drags a cross-court backhand into the tramlines.

As you were...

Oh hello! Dominic Thiem is 15-0 ahead on the Greek's serve and then drags him into an even baseline brawl. A high loopy backhand unsettles Thiem though and he goes long, before a forehand walloped long by Tsitsipas - his first unforced error of the set - gives Thiem a sniff at 15-30.

Thiem has some belief back as the pair slug it out again from the back of the court... the Austrian unleashes a stonking backhand which Tsitsipas can't control back to safety.

Two break points for Thiem...

Matthew Henry
BBC Sport at the O2 Arena

Thiem's support staff are throwing their fists around in the air, trying to get some life back into their players. If one of those swings caught you in the jaw it could knock you clean out. The Austrian desperately needs to find something more.

Thiem seems to be cruising towards a morale-boosting hold to love before he takes his eye off the ball - literally - and frames a forehand into the posh seats at the side of the court. That's 40-15.

Tsitsipas, never one to lack belief, claws back another point. Jingle jangle. How are your nerves Domi?

A collapse here could be curtains. Ah no, he's OK. An ace down the middle - which Tsitsipas unsuccessfully challenges - keeps him within touching distance.

Image source, EPA

Boris Becker
Three-time Wimbledon champion on BBC TV

Tsitsipas looks light on his feet now, where Thiem looks very heavy.

What has impressed me most about Tsitsipas this week has been his demeanour. Very calm and steady all week. Not getting too high in the good times, not getting too down on himself in bad times.

That extra bit of maturity has really benefitted him.

The way Tsitsipas has served today you'd back him to back up that break here. It's not a break until.. yes, yes.

The Greek makes sure it really is a break with a stunning service game. Four first serves land, four points are won. Thiem barely gets a string on the ball.

Bold stuff from Thiem and superbly executed to save the first break point. The Austrian plugs into the mains and destroys Tsitsipas' defence with some powerful hitting.

But then he crumbles in the next point with a meek return into the net.

Tsitsipas celebrates with plenty of restraint but he knows he is well in the driving seat here.

Uh oh. Thiem is swimming upstream again. A double fault - his first of the match actually - sees him trail 0-30 and leads to another rub of his face with a 'what the heck am I doing' type vibe.

A nice pick-up from his feet at the net gives the Austrian hope at 15-30 only for Tsitsipas to pounce on a second serve and bring up two more break points...

Thiem needed to survive a near eight-minute service game... Tsitsipas rattles through his in about 80 seconds. The Greek has been dominant on serve throughout the match, facing just two break points which he has saved, and comes through without little pressure from the other side of the net.

Image source, Reuters

Andrew Castle
BBC Sport tennis commentator at the O2 Arena

That was the best hold of the week for Dominic Thiem. How crucial will that be come the end of the match?

Sensational hold from Dominic Thiem. The Austrian knew he couldn't afford to fall behind early like he did in the second set and digs deep to palm off Tsitsipas and put some scoreboard pressure on the Greek.

Blimey! Thiem knocks the fluff off a forehand winner to fight off the first break point before a battle of the one-handed backhands - an exchange more beautiful and easier on the eye than a Picasso exhibition - ends when the Austrian goes long. Second break point for the Greek...

Thiem rightly challenges a line call to stay alive in the game, then bravely pins Tsitsipas back and draws the error out of his opponent. Back to deuce....

Matthew Henry
BBC Sport at the O2 Arena

The Greek flags are waving now. They sense the moment...