|2019 Nitto ATP Finals|
|Venue: O2 Arena, London Dates: 10-17 November|
|Coverage: Watch live coverage of one match per day on BBC TV, BBC iPlayer and online; Listen on BBC Radio 5 Live Sports Extra; Live text on selected matches on the BBC Sport website and app. Click here for Live Guide.|
Stefanos Tsitsipas reached the semi-finals of the ATP Finals, while Rafael Nadal produced a stunning comeback to boost his hopes of joining him.
As Nadal clawed his way back, Medvedev lost focus again, sarcastically giving a thumbs-up to his box as games slipped away.
After losing five successive games, the Russian settled himself to force a tie-break and was on serve at 4-5 in the breaker before he dragged a short forehand wide to give Nadal a mini-break and match point.
Another gruelling rally followed but a Medvedev shot that was originally called in was ruled out by Hawk-Eye to hand Nadal victory after two hours 49 minutes.
Medvedev can still qualify for the last four if he beats Zverev in two sets on Friday and Tsitsipas beats Nadal.
Tsitsipas dominates Zverev
Tsitsipas is the youngest player at this year’s ATP Finals, competing just a year after he won the NextGen tournament – the season-ending event for players aged 21 or under – but he produced a clinical, mature display to see off Zverev.
The pair were evenly matched in the first set until the Australian Open semi-finalist pounced when Zverev’s level dropped at 4-3, breaking serve and then closing out the match with his third game in a row.
Tsitsipas’ level increased further in the second set, hitting a backhand winner to bring up break point in the first game and then clinching it at the net after another well constructed point.
He broke again for 5-1 lead soon after with more immaculate tennis and even admitted afterwards he was “surprised” by his performance.
“I did everything right and once again it was not just me out there but a whole bunch of excited people who came to support me,” he said, referencing the strong support he received at the O2 Arena.
Zverev, meanwhile, was unable to find the high level that helped him sweep aside Nadal 6-2 6-4 on Monday.
The German lost his way badly after being broken in the first set and displayed negative body language on court.
He will still progress at Nadal’s expense if he beats Medvedev on Friday.