Will Federer win his seventh ATP World Tour Finals title?

A season that produced the biggest shake-up in men's tennis for more than a decade draws to a close next week with three ATP World Tour Finals debutants striving to sign off breakthrough years with a large exclamation mark.

US Open champion Marin Cilic, the man he beat in New York Kei Nishikori and Milos Raonic, the fresh-faced Canadian with dynamite in his serving arm, will all add plenty to the mix at the glitzy season-ender now in its sixth year of residence at London's eye-catching O2 Arena.

However, three of the world's established "big four" will be only too happy to slap down the young upstarts.

Serbia's Novak Djokovic is seeking a third consecutive title alongside the River Thames, one that would seal the world number one ranking and complete a memorable year for the 27-year-old who recently became a father for the first time.

Effervescent Roger Federer, at 33 the oldest player in the eight-man event, is targeting a seventh title at the ATP's blue riband tournament, and few would bet against the majestic 17-times GrandSslam champion achieving it.

Britain's Andy Murray, who produced a dazzling late surge to qualify for London with three titles in his last six tournaments, will also be hungry to launch himself into next year with a first ATP World Tour Finals crown.

And why not? After all, it has been a year of firsts.

"You know, there was Stan's (Wawrinka's) first Slam, Cilic's first Slam, Nishikori his first final, Raonic in the semis at Wimbledon," the Scot told reporters on Friday.

"The young guys have improved and got more consistent but they are up against some of the best players of all time so regardless of how much they have improved it's not going to be that easy to knock them off."

Murray, absent last year because of back surgery, will open the tournament on Sunday against Japan's Nishikori with Federer and Raonic, the other two members of Group B, facing off later.

Djokovic, unbeaten in 27 indoor matches, begins his Group A challenge on Monday against Cilic after Wawrinka takes on O2 regular Czech Tomas Berdych.

Djokovic warmed up for the tournament by retaining his Paris Masters title without dropping a set -- his first tournament since his wife Jelena gave birth to son Stefan.

"Maybe I should be making more children," a relaxed Djokovic told reporters. "Jelena won't like that!"

On the subject of new arrivals, Djokovic said the three first-timers in London underlined a sense of change in men's tennis which since 2003 has been dominated by Federer, the currently sidelined Rafael Nadal, himself and Murray.

"It's been a few years now that we've four different players winning the grand slam titles," said Djokovic who claimed a seventh major title at Wimbledon this year.

"There is some change in professional tennis in terms of new players and a new generation challenging the top four who have been winning most of the major titles but I think this is something normal to expect.

"Maybe we expected it a bit earlier."

Federer, twice a champion at the O2, said this year's Grand Slam roll of honour made for exciting times, while firing a subtle psychological salvo at Raonic who he lost to at the Paris Masters last week.

"It's nice to see new faces out there with Raonic, Cilic and Nishikori," the Swiss told reporters.

"We'll see how it plays out this week. You really don't want to lose your first match in the group because then it's out of your hands. I lost to Milos in Paris because he played well, but it's more up to me than him. Looking forward to a re-match."

Raonic was outclassed by Federer in the Wimbledon semi-finals this year but it has still been a superb year for the Canadian who reached as high as world number six in July.

"This is going to be a new challenge because, as he's been here many times, I will have to find my game straight away," the 23-year-old Raonic predicted.

Croatian Cilic, still not completely recovered from a nagging shoulder problem, said his win at the US Open, and Wawrinka's over Nadal at the Australian Open, had given "new breath" to the ATP Tour.

"I'm really honoured to be here, it's been an incredible season," he said. "I feel the door opened a little for the other guys, the second line of players, this year. Maybe we are going to see more new Grand Slam winners next year."

For the time being though, a $1.9 million cheque is up for grabs for an undefeated champion in London and few would bet against one of the "old guard" walking off with it.