Six-time champion Roger Federer survived a late-night Swiss semi-final thriller against Stanislas Wawrinka to set up an ATP World Tour Finals showdown against Novak Djokovic.
After a week of one-sided group stage action at London's O2 Arena, the season-ender burst to life with world number one Djokovic battling past Japan's Kei Nishikori after a mid-match meltdown before Federer saved four match points in a near three-hour duel with compatriot Wawrinka.
Federer eventually prevailed 4-6, 7-5, 7-6 against the man he will join forces with when Switzerland take on France in next week's Davis Cup final.
Djokovic, bidding for a third consecutive season-ending title having already secured the number one ranking, beat Asian trailblazer Nishikori 6-1, 3-6, 6-0 after losing his cool with another capacity crowd at the O2 Arena.
Djokoviv, who has already clinched the year-end world number one ranking, can become the first man since Ivan Lendl (1985-87) to claim three consecutive Tour Finals crowns if he wins on Sunday against either Roger Federer or Wawrinka, who face each other later in an all-Swiss semi-final.