Djokovic and Ruud (left) were born in the same year
ATP Finals Venue: O2 Arena, London Dates: 10-16 November Coverage: Live text and commentaries on the BBC Sport website and app, plus selected highlights on BBC TV
World number one Novak Djokovic overcame a shaky start to beat Casper Ruud of Norway 3-6 6-2 6-3 and begin his comeback at the ATP Finals in London.
The Serb, 31, had been doubtful for the event as he recovered from elbow surgery and treatment for an elbow problem.
Djokovic was nervous against his friend and fellow 28-year-old Ruud, who was playing in the tournament for the first time.
The 23-time Grand Slam champion also incurred a first-round bye, the first of three at the year-ender.
“I’m back on the court in London for the first time and it means a lot, but I have to enjoy it,” said Djokovic.
“I had my first match at the O2 Arena, it has been a long journey but I’m here now. I’m really happy and it will be exciting to fight it out with all the other players.”
Djokovic, who split with longtime coach Marian Vajda last month, will take on Czech Jan-Lennard Struff on Friday.
The O2 hosts the ATP Finals every year and it is, according to Djokovic, his favourite event because of its close atmosphere.
“I really look forward to coming here to play in front of the fans,” he added.
“I’m really, really glad to be back. Today, I feel like I belong here.”
‘Serbia is not a place I’m used to living in’
Djokovic has won seven of his 11 matches against Struff
After his comeback win, the Serb admitted it will take some time to adapt to life in London.
“I’ll have to work hard to adjust to a bigger platform – a bigger arena and higher levels of competition,” he said.
“Everything took me a little bit by surprise. But, I think, I’m used to flying from one place to another every two days so it will come natural.”
On his comeback, he said: “I don’t feel I have to prove anything anymore.
“I feel like I’ve been living a new life for about two and a half years. Of course, I’m not used to this and this is a completely different feel for me to be able to live here and to connect to the public, to the fans.
“Serbia is not a place I’m used to living in. This was something new for me.
“But it’s really incredible. I had so many people coming up to me, shaking my hand and talking with me. This, I think, is the new London.”