Hello and welcome to live updates of the second match of the 2017 Nitto ATP World Tour finals. It's rising star and world No.3, Alexander Zverev against 2014 US Open champion, Marin Cilic in Boris Becker group.

GAME, SET AND MATCH! - ZVEREV 6-4 3-6 6-4 CILIC. What a turnaround. Zverev comes out all guns blazing, firing a pair of supreme winners to tee up triple match point. The young German doesn't let up there, sealing it on the first with a thumping put-away at the net to cap his debut here with a victory in two hours and five minutes. It was a real rollercoaster but at the end of it all, he joins Federer at the top of Boris Becker group after the first of the round-robin matches.

ZVEREV 6-4 3-6 5-4 CILIC. That's a welcome love hold at such a big juncture in this contest. Zverev playing with real authority there. Cilic must hold now to stay in the match.

ZVEREV 6-4 3-6 4-4 CILIC. Good response from Marin. The trusty serve plays its part as he levels up at the business end of the match. Whoever blinks now will surely lose.

ZVEREV 6-4 3-6 4-3 CILIC. Zverev has found an extra gear at a crucial moment in the match. He blitzes through a love hold. Pressure on Cilic now. He's been the better player for most of the match, but we saw what happened when Zverev had a purple patch at the start of the opening set.

BREAK! - ZVEREV 6-4 3-6 3-3 CILIC. Wow, has the momentum swung back to Zverev? At 40-15 down he hurls his racket to the floor. It's usually a bad sign, but it seems to inspire him. He corks a backhand winner down the line of the next point and then plays some scintillating tennis at the net to make deuce and storm through to break back.

ZVEREV 6-4 3-6 2-3 CILIC. Great fight and spirit from Sascha. At 0-30 it looks bleak, but he keeps his fading hopes alive to battle through a hold from deuce.

ZVEREV 6-4 3-6 1-3 CILIC. Marvellous from Marin. The Croatian consolidates, producing some magic hands at the net to provide a block volley winner after Zverev had threatened to force deuce from 40-0 down.

BREAK! - ZVEREV 6-4 3-6 1-2 CILIC. Cilic unleashes a stonking crosscourt forehand pass to make 30-30 and is then gifted the break courtesy of two untimely errors from Zverez. Both players have gone for it at the start of this set, but it's the Croatian who has delivered.

ZVEREV 6-4 3-6 1-1 CILIC. Excellent back up play to make the most of that big serve. Cilic remains unfazed by Zverev's vibrant start to set 3 and eases to a hold to 15 to move level. It's developed into a very watch-able showdown.

ZVEREV 6-4 3-6 1-0 CILIC. Zverev comes out fired up and starts the decider in positive fashion. Cue some fist pumps and a bit of psychology. Will it affect Cilic? Probably not. He just needs to keep doing what he's done for the past set and a half.

SET! - ZVEREV 6-4 3-6 CILIC. It's all square! Cilic holds his nerve, fighting back from 15-30 to deservedly serve out a set in which he was the much more consistent and attack-minded player. Zverev has leaked far too many errors since his barnstorming start to the match. The smart money would be on Cilic right now, but don't rule out another purple patch from the German youngster.

ZVEREV 6-4 3-5 CILIC. Sascha working hard just to keep this set alive. He ventures into the net to despatch an overhead to save set point before a couple of solid serves help him over the line. Cilic to serve for it next.

ZVEREV 6-4 2-5 CILIC. The pattern continues. Zverev pushed on serve while Cilic breezes through his, this time with another love hold. He's one away from levelling the match.

ZVEREV 6-4 2-4 CILIC. Zverev refuses to cave as Cilic presses for what would surely be a set-clinching double break. The Croatian can't quite conjure up the BP as he overcooks to the baseline to let Sascha off the hook from deuce.

ZVEREV 6-4 1-4 CILIC. This is looking all set for a decider. Cilic surges to a love hold, finishing with an ace as Zverez continues to toil.

ZVEREV 6-4 1-3 CILIC. A corker of a crosscourt winner off that vicious two-handed backhand claims a solid hold to 15 to stop the rot and get Zverev on the board.