Our man at The O2, Andy Schooler, previews Tuesday's play, including Roger Federer v Alexander Zverev.
Marin Cilic v Jack Sock (1400 GMT, Sky Sports Arena & BBC Two)
Head to head – Overall: 0-2; Indoor hard: 0-0; 2017: 0-0
Cilic must still be wondering how he didn’t finish off Alex Zverev on Sunday night having been the better player for the vast majority of it.
However, a poor start and an even worse finish saw him lose out and, with Roger Federer to play after this, he now faces an uphill battle to reach the semi-finals.
One break of serve in the first game and an untimely double-fault in the second-set tie-break ultimately cost Sock against Federer in his opener when his serve and forehand were in pretty decent working order.
Federer’s movement is considerably better than Cilic’s and I’d expect Sock to use his power to try to outmanoeuvre his opponent. He’s done so successfully in the past, winning both of their previous meetings and the underdog looks to have a decent chance here.
A good way to support him may well be in the aces market. In both previous meetings, it is the American who has finished with more, while he served well against Federer, losing his delivery only once and out-acing the Swiss 11-5.
Verdict: Sock to win 2-0
Best bet: Sock to serve the most aces at 11/8
What the players say
Cilic: “I'm going to play Jack next match. I believe I need to win that one to give myself a chance to go through. Well, one positive thing today is that I won a set in the match that I lost, so it could maybe make a difference towards the end (of the group stage).
“It's a slightly different tournament than what we were used to. Even with the loss, you can go through. I'm just going to try to stay positive and focus on the next match.”
Sock: “It will be different (to playing Federer) for sure. Roger puts a pressure on you that I feel no other player really does.
“I'll definitely be able to maybe hit my way into the next few matches, have some longer rallies, not feel sort of the presence he puts on you when you're out there.
“I can take stuff away from those matches where I've had the wins (against Cilic) and apply it.”
Roger Federer v Alex Zverev (2000 GMT, Sky Sports Arena)
Head to head – Overall: 2-2; Indoor hard: 0-0; 2017: 1-1 (RF in Halle; AZ in Montreal; AZ also won at Hopman Cup, not on official records)
Federer clearly deserves favouritism is a sentence that I expect will apply to all of his matches this week.
He did all that was asked of him against Jack Sock on Sunday when he didn’t face a single break point. That’s now happened in five of his last seven matches.
Federer wasn’t at his brilliant best but he was clearly the better player and felt afterwards he would only improve having shaken off some rust.
Zverev produced a lot of errors in his opening match and really should have lost to Marin Cilic having been second best for long periods.
He’s caused Federer problems before but he’ll need a big improvement if he is to do so again.
One suspects Federer will also be looking to put the young gun in his place, particularly given he lost the Montreal final to him in frustrating circumstances, a back injury hindering him in that defeat.
He's heavily odds-on to win though so I'll take another look at the aces market. Zverev's figures in their previous meetings make pretty convincing reading - the German has served more in all five matches. And things aren't getting better with age - Zverev has had 17-9 and 6-2 margins this year.
Verdict: Federer to win 2-0
Best bet: Zverev to serve the most aces at 8/13
What the players say
Federer (after beating Sock): “This is the best I've felt since the Del Potro final (in Basel). I'm very happy to see that I didn't have to pay the price for taking it easy, you know, resting, recovering.
“Now I think I'm in the tournament. Now there's no more turning back. Just full steam ahead every match that comes.”
Zverev: “I think anyone beating Federer in this group has a good chance of passing (into the semi-finals). But he's the favourite, definitely, in all of the matches he plays.
“I played him a few times this year now. I played him three times, if you count the Hopman Cup match we played (winning twice). Obviously, all of them were great matches. Hopefully it can be another one.”
Doubles matches
Henri Kontinen & John Peers v Jean-Julien Rojer & Horia Tecau - 1200 GMT
Pierre-Hugues Herbert & Nicolas Mahut v Ryan Harrison & Michael Venus - 1800 GMT
