SINGAPORE: Germany’s Angelique Kerber criticised the format of the WTA Finals after she became distracted by qualifying permutations and exited the lucrative end-of-season event following a straight sets defeat by Lucie Safarova.

The world number seven had the advantage of knowing she only needed to take a set off the already eliminated Czech to reach the semis after watching Spain's Garbine Muguruza beat Petra Kvitova 6-4 4-6 7-5 in the penultimate White Group contest.

Yet the German looked unsettled and offered her worst display of the week as she was well beaten 6-4 6-3 at the Singapore Indoor Stadium on Friday.

"I think it's not fair, because I think it's like in the football. Like when it's really counting for something, you should play like the same time," the 27-year-old German told reporters.

"I was actually trying to be in my tunnel and just focussing on my match. I told everybody I'm not counting. I will go out and play my match. They were counting. 'Okay, she won one set, now you must win just one set'."

Final round matches in football tournaments are played at the same time to ensure all teams chase the win, while avoiding the possibility of opponents making pacts to guarantee qualification.

Football's world governing body FIFA adopted the policy after West Germany beat Austria 1-0 at the 1982 World Cup which meant both sides went through at the expense of Algeria.

"I think it's fairer like in football if you play in the same time," Kerber said.

However, the Singapore Indoor Stadium, in its second year of a five-year deal to host the elite eight-woman WTA Finals, only has space for one court.

Kerber, who won four titles this year, said she understood the limitations but felt the idea should be considered.

The German, who beat Kvitova earlier in the week but lost to Muguruza, was more frustrated with her failure to deliver when it was needed most.

"I mean, you have days like that. I will just try to forget the match as soon as possible," she said.

"At the end, I had amazing week here. I will just take the positive things to the next week, to my holidays, and, yeah, try to improve my game and everything for the next year."