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 6-7 4-6 DEL PORTO. Extraordinary! He's done it! For only the second time in his career, Juan Martin del Potro has come from two sets down to win. You would not have given him a chance at 0-2 but the Argentine has rallied remarkably to clinch one of the victories of his career.

An hour after he saved match point, Del Potro has a match point of his own when Thiem sends a wild forehand long and wide. A breathless rally ends with a hammer Del Potro forehand finding the net and we're back to deuce. Del Porto brings up another MP though and Thiem ends on a disappointing note, double faulting. The Austrian competed fabulously and deserved to end on a better note. But all eyes are on Del Potro...

THIEM 6-1 6-2 1-6 6-7 4-5 DEL PORTO. Thiem has a golden chance to take the game to deuce when the ball sits up off the net...but he sees red and overcooks it, firing a ferocious forehand wide of the tramlines. The mistake seals another hold for Del Potro, who is now a game away from victory.

THIEM 6-1 6-2 1-6 6-7 4-4 DEL PORTO. There was a danger that Del Potro could run away with this set but Thiem shows what he is made of again, clinching another dominant service game. The majority of Grandstand appears to be cheering for the Argentine, who continues to dazzle on his forehand, but Thiem is as dogged as he is talented.

THIEM 6-1 6-2 1-6 6-7 3-3 DEL PORTO. Dominic Thiem backs off a little and Del Porto senses blood, racing to three break points. But the Austrian saves all three, the last with a pinpoint, nerveless forehand into the corner, and he clinches a crucial hold with a beautiful down-the-line backhand. That was some comeback. You cannot take your eyes off this match.

THIEM 6-1 6-2 1-6 6-7 2-2 DEL PORTO. This is only the seventh five-set match of Thiem's career -- he is pegged at 3-3 -- and you wonder if Del Porto's superior experience will tell in the decider... No sign of that so far, though, and Thiem holds to love to keep it on serve. The Argentine has been given another magic pill by the doctor. Will it work wonders?

THIEM 6-1 6-2 1-6 6-7 1-1 DEL PORTO. Anything you can do... Great resistance again from Thiem, who responds with a love hold, sealed by a clinical wide ace.

THIEM 6-1 6-2 1-6 6-7 0-1 DEL PORTO. Del Porto continues where he left off in the last set and, remarkably, leads for the first time in the match. He holds with help from a seventh ace.

THIEM 6-1 6-2 1-6 6-7(1) DEL PORTO. Pandemonium on Grandstand as Del Porto ensures this match will go the distance, clinching the tiebreak 7-1. The momentum is firmly with the Argentine now, who came back from 5-2 down in that fourth set. The best match of the championship so far.

THIEM 6-1 6-2 1-6 6-5 DEL PORTO. Grandstand is euphoric as Del Porto holds a 5-1 lead at the changeover. A shanked backhand into the stands by Thiem sums up the Austrian's tie-break. He has tried to overpower Del Porto, which was never going to work.

THIEM 6-1 6-2 1-6 6-6 DEL PORTO. Remarkable! A couple of hammer forehands help Thiem to two match points and the Austrian appears -- at last -- to be closing in on victory. But Del Porto is never beaten. He saves both with aces, the first 127mph, and goes on to clinch the game and set-up a tie-break.

THIEM 6-1 6-2 1-6 6-5 DEL PORTO: Impressive retaliation from Dominic Thiem, who recovers some rhythm and confidence with a strong hold. A deft drop shot at the net from the 6th seed suggests his nerves are quite recovered from the shock of that break. For the third time, Del Porto will serve to keep this match alive.