Former world No 1 Jelena Jankovic appeared to question Serena Williams' sportsmanship after losing a close three-set match to the game's leading player in the semifinals of the WTA Championships.

Williams, who claimed to be exhausted near the end of a long season, reacted with fretful and sometimes distracting behavior while struggling to a 6-4, 2-6, 6-4 two-hour win over Jankovic.

It included weeping into her towel, gesticulating and arm-waving, bending over and slumping, yelling and calling out, and both moving during the rallies and conducting the game at different speeds.