Serena makes last four in Istanbul
Serena Williams became the first player to reach the semi-finals of the WTA Championships with another dominant display in Istanbul.
The world number one went into the end-of-season tournament as the hot favourite to retain her title and three comfortable round-robin victories have only enhanced her status.
This time her opponent was fifth seed Petra Kvitova, who won the title at the Sinan Erdem Dome in 2011 and impressed in beating Agnieszka Radwanska in her first match.
But the Czech did not live up to her billing as Williams eased to a 6-2 6-3 victory to guarantee top spot in the red group.
Had Kvitova taken any of the three break points she created in the first game, it might have been a different story, but Williams saved them all.
The American then broke serve immediately and again in the eighth game to clinch the opening set.
Williams' all-round level was simply a cut above, as it has been in virtually every match this season.
Kvitova made too many errors to put any real pressure on, and when it looked like she might one of Williams' 11 aces usually helped the defending champion out.
Williams did not lose a match in both her most recent appearances at this tournament in 2009 and 2012 and Thursday's night's win took her run of successive victories to 13, second only to Martina Navratilova's 21.
Kvitova, who has now failed to beat Williams in all five of their meetings, will still qualify for the semi-finals if she beats Germany's Angelique Kerber on Friday.
She may appear unbeatable, but the 32-year-old said: "When I play top players or a grand slam winner, such as Kvitova, who has such a dangerous game, you've got to go in there knowing that anything can happen and I have to be really focused. That was just what I did.
"I would say my focus is what's pleasing me most of all."
Asked about the first game of the match, Williams said: "Something told me to hold serve in that game, and I'm glad I did. It could have definitely changed things. I could still be out there. I really just dug deep and tried to hold."
- Council chiefs call for safety talks with taxi drivers
- Woman left to foot bill for driving over bollard
- Mother 'gobsmacked' at having to pay for lost property
- Shopping centre bosses apologise over new car park system chaos
- Head speaks out on school's fine system
- Dog owner in court after woman attacked