Japan’s Kei Nishikori admitted he had to overcome severe stagefright before his ATP Tour Finals debut with an impressive 6-4 6-4 victory over Andy Murray – his first career win over the Scot in four attempts.

Nishikori is the first Asian singles player to qualify for the prestigious season-ending tournament, but his emotions took over initially in front of a capacity 17,500-crowd at London’s O2 Arena.

After a tense start, Nishikori eventually rose to the occasion and was dominant in defeating home favourite Murray.

“The stadium is huge and I tried not to look up too much because there were so many people on the top tier. I just tried to stay focused,” Nishikori said.

“Maybe when I walked into the stadium I was nervous but, at the same time, I was really excited to play with this crowd.

“I was thinking, I’m very honoured to be here for the first time as a top-eight player.

“I was a little bit tight in the beginning, so I was really happy that I played good tennis in this situation. I tried to stay calm …”

With matches against Roger Federer and Milos Raonic to come, Nishikori still has plenty to do to reach the semi-finals but he sees no reason why he can’t advance beyond the group stage.

“I hope so. There is still a long way to going to the final and to win it, but that’s what I’m trying to aim for.

“I was little bit surprised at how I played, very confident. Now I’m very much looking forward to the next match.”

Nishikori reached his first grand slam final at the US Open and became the first Asian man to finish in the world’s top 10 since 1973 with 52 wins this season.

Despite losing the New York final to Marin Cilic, Nishikori went on to win tournaments in Kuala Lumper and Tokyo to climb to world No.5.

He puts his success down to finally persuading himself that he has no reason to feel inferior to the top stars.

“Yeah, I was struggling with that actually because, when I was junior, I wasn’t thinking too much, so I was able to play good tennis with anyone. But after turning pro, I was feeling a lot of respect to everybody, especially top players,” Nishikori said.