For the second straight year at the World Tour Finals, an all-Swiss semifinal between Roger Federer and Stan Wawrinka will take place. The 2014 installment did not disappoint, as Federer outlasted his countryman in a third-set tiebreaker at the end of a heated, controversial battle.

Roger Federer and Stan Wawrinka will be facing each other for the 21st time in their careers when they battle for a place in the World Tour Finals title match on Saturday night.

Federer is dominating the head-to-head series 17-3, but what was once the most lopsided and least interesting “rivalries” in all of tennis has reinvented itself over the last 17 months. Wawrinka has won two of their last six meetings–in the 2014 Monte-Carlo final and in the quarters of the French Open this spring.

Their showdown at the same stage of this same event last year will not soon be forgotten. Federer saved…