Zverev says length of season is 'ridiculous'

Prior to this though, we have two matches in the Kuerten Group, with Novak Djokovic and Alexander Zverev meeting at around 1400 United Kingdom time, to get proceedings underway.

There was much hope that yesterday's match between the two players would make for a rare competitive encounter at The O2 arena, but the world No 1 Djokovic took full advantage of a Zverev capitulation to triumph 6-4, 6-1 in 67 minutes.

"I guess winning the first set really counts this year", Djokovic said.

It was the 31-year-old Serb's second comfortable win in the Gustavo Kuerten group and combined with Marin Cilic's 6-7 (2) 6-3 6-4 defeat of American John Isner later in the day, he sealed his place in the semi-finals at the year-ender for the eighth time.

Djokovic will now play Zverev on Wednesday afternoon with the victor likely to top their group, named after Brazilian clay court ace Guga Kuerten.

He is plotting a return to action in Brisbane in 2019, but rocked up to the O2 to catch a glimpse of the action at a tournament he won to secure the year-end No. 1 spot two years ago. "I played well midway through the second set and started to swing through the ball", said Djokovic, who has suffered only two defeats in the Finals since 2012.

Further errors from Cilic saw Zverev race to a 5-1 lead before a classy backhand victor and a unreturnable serve sealed the second-set tiebreak, as well as the opening win. "Whether I think the structure of the ATP specifically can be better, I actually do". Kyle Steven Morgan, I love you bro.

However, Zverev had the first two break point opportunities at 4-4 after Djokovic double-faulted, but the Wimbledon and US Open champion escaped with a drop shot to remain ahead.

Zverev said earlier this week he won't be representing Germany because it's too tough an ask so late in the year.

Zverev had finished an otherwise extremely tidy opening set with a first double-fault to hand the initiative to Djokovic, and he simply could not wrestle it back.

"I think the date is very important and I think none of the top players will play, except Rafa (Nadal) because it's in Spain". Zverev is obviously the leader of that next generation. He has won many Masters events already, I think three in his career, which is quite impressive. He has proven himself. Then you have players like (Karen) Khachanov, of course, (Stefanos) Tsitsipas, (Borna) Coric.

He would, Djokovic said on court, look forward to some downtime with his family until his next match on Friday, but he will surely also fit in a couple of hours' tennis viewing to see just how that evening match pans out.