Casper Ruud will face Daniil Medvedev in the last four of the ATP Finals after coming from behind to beat Andrey Rublev 2-6, 7-5, 7-6 (7/5) on Friday, while Djokovic closed out the Green Group with a 6-2, 6-1 destruction of Cameron Norrie.
Both Ruud and Rublev knew a win at the Pala Alpitour in Turin would take them into the Saturday's semi-finals and Ruud impressed in coming from behind to make sure he will be taking on the world number two.
The Norwegian has followed up a brilliant year in which he won five tournaments by reaching the semis in his first appearance at the season-ending event.
He did it despite being demolished in the first set by fifth seed Rublev, who then looked certain to be facing his countryman at the weekend after breaking Ruud's serve in game three of the second set.
"It's a great day for me and my career obviously, this year has been special," said Ruud on court.
"I've been on the edge for the past two matches, coming back from a set down... I don't know really how I did it.
"I got some good returns and then the momentum changes, we are both playing with nerves in the end so I guess I can thank my arm I was able to hit an ace on the match point because I was so nervous."
Fifth seed Rublev came into the match unbeaten in his four previous meetings with Ruud but after a strong start fell to a deserved defeat, failing to qualify for the knockout rounds from the Green Group.
"I don't have much to say, it's tough. Hopefully I can get through it to give myself a lesson." a dejected Rublev later told reporters.
- Djokovic dominates -
Djokovic showed just how difficult it will be to stop him from winning a record-equalling sixth Finals title in his straight sets demolition of Briton Norrie, who leaves the tournament without a win under his belt after replacing injured Stefanos Tsitsipas.
World number one Djokovic broke Norrie in the first game of the evening and from then on blitzed the 26-year-old, who barely laid a glove on the 20-time Grand Slam winner in a match which lasted just over an hour.
He barely broke a sweat, winning every one of his service games and breaking Norrie five times in a typically dominating display from the Serb ahead of his semi-final showdown with third seed Alexander Zverev on Saturday night.
Djokovic was in good spirits after the match and after a breezy post-match interview carried out exclusively in Italian he batted a few balls into a crowd who will almost certainly be supporting him in Saturday’s semi.
"I played very ell from the first to the last point... There weren't many negatives to my play,” said Djokovic in Italian on the court.
“Tomorrow's going to be a hard match, he's a tough player who is very tall and has one of the best serves in the world... Let's see, I'm expecting a match which asks a lot of me physically, mentally. It’s always like that with him but I'll do everything to win.”