The fourth and final match on Grandstand is a big one. It pits No.6 seed Dominic Thiem with 2009 US Open winner, Juan Martin Del Potro.

THIEM 6-1 6-2 1-6 5-5 DEL PORTO. That's how you do it! A love hold for Del Porto, assisted by more errors by Thiem. The Austrian is going to have to regroup quickly to avoid a collapse here.

THIEM 6-1 6-2 1-6 4-5 DEL PORTO. 'Diego, Diego, Diego,' chants the partisan crowd on Grandstand as the 24th seed steps up to serve.

THIEM 6-1 6-2 1-6 4-5 DEL POTRO. 30-0 down and staring defeat in the face, Del Porto pulls out one of the best passing shots of the match, belting a backhand winner down the line. It shifts the momentum, and suddenly the Argentine has a break point. Thiem's nerve fails and he scoops a forehand long.

Ashe erupts and Del Porto will serve to level the fourth set. Incredible.

THIEM 6-1 6-2 1-6 3-5 DEL POTRO. Del Potro is not going quietly. He forces Thiem to serve for the match, clinching a gusty game which included his quickest serve of the evening at 128mph.

THIEM 6-1 6-2 1-6 5-2 DEL POTRO. It's four in a row for Thiem who has hit a purple patch just when he needed it. He holds to 15 and is one game away from the last eight.

BREAK! - THIEM 6-1 6-2 1-6 4-2 DEL POTRO. Plenty of fist pumps from Thiem as he turns the screw with some deft touches at the net. He goes on the attack again at deuce and unloads a superb backhand down the line to earn what could be a hugely significant break.

THIEM 6-1 6-2 1-6 3-2 DEL POTRO. Thiem somehow wrestles the pendulum of momentum so it swings back his way. He's playing thinking man's tennis right now after a good half an hour where he must have felt foggy and flat-footed.

BREAK! - THIEM 6-1 6-2 1-6 2-2 DEL POTRO. A huge moment for Thiem. He was on the rack there, but dug in and found some real depth and consistency on his shots to immediately break back.

BREAK! - THIEM 6-1 6-2 1-6 1-2 DEL POTRO. This is a sensational turnaround. Delpo has the momentum right behind him and Thiem doesn't quite know what to do. He continues to miss the lines with his forehand and pays the price as Delpo gets the early breakthrough. Whisper is quietly, but a fifth-set decider may be on the cards....

THIEM 6-1 6-2 1-6 1-1 DEL POTRO. Thiem can only block a return long as Delpo recovers from 15-30 to move level.

THIEM 6-1 6-2 1-6 1-0 DEL POTRO. Thiem has pressed reset after that third set nightmare and has regained some form. He holds to love to earn himself the scoreboard advantage.

SET! - THIEM 6-1 6-2 1-6 DEL POTRO. The Argentine reduces the arrears, serving it out to 30 for a breadstick.

Meanwhile, in the men's doubles...

BREAK! - THIEM 6-1 6-2 1-5 DEL POTRO. Delpo breaks again! What a turnaround! He will now serve for the third set.

THIEM 6-1 6-2 1-4 DEL POTRO. The Argentine No.24 seed maintains his momentum with a solid hold to 15.