Roger Federer moved into the ATP Finals last four at the expense of Novak Djokovic with a scintillating win over his great rival at the O2 Arena.
Swiss third seed Federer, 38, won 6-4 6-3 in a round-robin match which eliminates the Serb second seed from the season-ending tournament in London.
Federer will meet top seed Rafael Nadal or Stefanos Tsitsipas in the last four.
Djokovic's defeat also means Spain's Nadal is guaranteed to finish as the year-end world number one.
More to follow.