London - Roger Federer will face Novak Djokovic in the World Tour Final after defeating Swiss compatriot Stan Wawrinka 7-5, 6-3 on Saturday.
Earlier, Serbian world number one Djokovic beat Spain's resurgent Rafael Nadal 6-3, 6-3 in his semi-final to secure his place in Sunday's title match.
Third seed Federer beat Djokovic in straight sets in the group stage.
"A great match, I really enjoyed it," Federer said after his win on the hard court of London's O2 Arena.
"It will be a perfect ending only if I win. Novak should be knocked out by now! No, I am joking. He played a great match against Rafa earlier today and I'm sure it will be a fantastic meeting."
The clash was a repeat of last year's semi-final, which ended in bad blood between the two Switzerland team-mates.
In the 2014 semis, they embarked on one of the most draining matches of the season -- nearly three hours of cut-throat tennis that Federer won 4-6, 7-5, 7-6 (8/6) after saving four match points along the way.
On top of that, there was a bust-up -- Wawrinka taking umbrage at what he saw as inappropriate words from Federer's wife Mirka from the players' box at a key point in the third set.
But the pair appeared to patch up their differences, teaming up to win a first Davis Cup for Switzerland.
Federer went into the Wawrinka match with a 17-3 lead in career clashes between the two, including all their matches on a hard court.
He won two of their three matches this year, including their last encounter in the US Open semi-finals, where Federer went on to lose to Djokovic.
At the coin toss, the umpire, like a boxing referee, asked both players for "a clean fight" and "no blows below the belt". Federer just about managed to raise a smile.
Fourth seed Wawrinka broke first for a 3-2 lead thanks to some luck at the net cord, flicking a shot into Federer's face and then diverting a shot wide from the 17-time Grand Slam champion.
But Federer broke back to level at 4-4 and motored on to take the first set, breaking again as Wawrinka double-faulted and misfired, a volley into the net sealing matters.
Federer broke in the second game of the second set and had two break points in the fourth before Wawrinka pulled it back.
Wawrinka saw off a match point to hold for 5-3, but Federer was cruising by this point and ended the contest with a straightforward service game.
The pair shook hands warmly at the net.