Daniil Medvedev booked his place in the last four of the ATP Finals on Wednesday after beating Alexander Zverev 7-6 (9/7), 6-4, while Carlos Alcaraz cruised past troubled Andrey Rublev to get his campaign up and running.
World number three Medvedev had to win in straight sets to claim a spot in the semi-finals in Turin with a match to spare and he saw off big-hitting German Zverev in a stodgy Red Group encounter.
He faces Carlos Alcaraz, a 7-5, 6-2 winner earlier in the day, in his final match and has the world number two's last-four hopes in his hands.
"I hope that I feel well tomorrow and ready to fight because this tournament is tricky," said Medvedev.
"I'm into the semis but you want to keep the rhythm and against Carlos... if we play at night you don't want to finish 7-6 in the third (set) at midnight. I just hope I can show my best tennis."
Medvedev has a long-running rivalry with Zverev, the pair not getting on off-court, and he has now prevailed in five of their six matches this season.
One of those wins came on his way to his surprise triumph at the clay-court Italian Open back in May, one of five titles won by Medvedev this year.
The 2020 champion looks in fine form despite Wednesday's match being his 82nd this year and will cause serious trouble to whoever he faces in the next round.
Zverev, a two-time winner at the season-ending tournament, would have qualified from the Red Group with a win of either sort following Alcaraz's earlier victory.
The 26-year-old hit more aces and winners than Medvedev but still ended up on the wrong side of the result after throwing away his service game to save the match.
Zverev can still make it through though and in his final match will face a dejected Rublev, who is yet to win a set at the Pala Alpitour.
- Alcaraz back on form -
World number two Alcaraz has had problems with his form and fitness over the past few months and was staring at possible early elimination after losing his first match with Zverev.
But he looked in much better condition on Wednesday and comfortably claimed his first ever win in the season-ending tournament, snapping a three-match losing streak to boot.
"I'm really happy to show this level and realise that my level is still there, giving myself a chance in this tournament," Alcaraz told reporters.
"After this win, everything has changed in my mind."
The 20-year-old easily dealt with Russian Rublev who once again failed to make his mark in a big match with one of tennis' leading lights, and lost control of his emotions after giving away a service game at the start of the second set.
Being one set and a break down was too much for the 26-year-old who then repeatedly smashed his racket into his left knee, drawing blood, and soon after gave into his anger and promptly collapsed just as he did in his opening defeat to long-time friend Medvedev.
Afterwards Rublev brushed off the assault on his own limb as "nothing" but then admitted that he is struggling emotionally with what has been a hard end to the season.
On Thursday Jannik Sinner will try to become the first Italian to reach the semi-finals when he takes on Holger Rune in the tight Green Group.
Straight victories over now-retired Stefanos Tsitsipas and Novak Djokovic might not be enough to secure a spot in the next round.
And Sinner faces Rune who only had to play three games against Tsitsipas who dropped out with injury.
Sinner meanwhile prevailed on Tuesday in a three-hour thriller with Djokovic, who plays Tsitsipas' replacement Hubert Hurkacz with his last-four spot also still in the balance.
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