Casper Ruud revealed his approach was to "fight fire with fire" in his huge win over Andrey Rublev at the ATP Finals and is already relishing getting a shot at Daniil Medvedev.

The Norwegian has enjoyed a fine 2021, winning five ATP Tour titles, and has now moved into the semi-finals in Turin on his debut appearance at the prestigious year-ending event.

Ruud appeared to be on the way out when he was trailing by a set and a break against Rublev, having lost all four of the previous meetings between the pair.

But he fought back to win 2-6 7-5 7-6 (7-5) on Friday and extend his impressive season by at least one more match.

"The court is playing very fast and Andrey plays very fast," said Ruud, who triumphed despite only winning 98 of the 208 points played in an intense battle where his Russian opponent also impressed.

"He rips the ball harder than anyone on the tour and serves very well on his first serve. 

"We all want to play under control and with initiative, but it is not easy against Rublev because he makes you run and play defensively all the time. 

"I knew I had to fight fire with fire. 

"On the big points, I think I played quite smartly."

Aside from Ruud, the other three semi-finalists (Medvedev, Novak Djokovic and Alexander Zverev) are all former ATP Finals winners, making this event the first since 1994 where that has happened.

US Open champion Medvedev represents a daunting challenge in the last four for Ruud, who bounced back from an opening Green Group loss to Djokovic by beating alternate Cameron Norrie before his high-quality winner-takes-all clash with Rublev.

"I am looking forward to Saturday already – it is going to be another tough battle," said the 22-year-old after firing down 14 aces in his victory.

"Medvedev is a different kind of player to Rublev. He is one of the best in the world, and he has proven himself as one of the best over the past two or three years. 

"I have played against him a couple of times and lost both, but I know a little bit about what I am going to face, and it is going to be a fun challenge.

"I am just enjoying the moment."

Two of the last three players to reach the last four on debut at the ATP Finals have gone on to win the tournament, Grigor Dimitrov (2017) and Stefanos Tsitsipas (2019).

Ruud will dream of replicating that duo, but Rublev must come to terms with a second consecutive group-stage exit in the ATP Finals.

"It is tough," Rublev said. "Hopefully I can get through it to get a good lesson, which will give me a huge improvement.

"In the moment, I got tight, which is normal. Casper played well. He has a great forehand – one of the best on tour."