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'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," said Medvedev.

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.

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. (AFP)