Istanbul - Victoria Azarenka at last made sure of the year-end world number one ranking, just two matches from the finish of the 2012 season, when she overcame Li Na to reach the WTA Championships semi-finals Friday.
The Australian Open champion from Belarus claimed a 7-6 (7/4), 6-3 win over the Chinese star to set-up a last-four clash on Saturday against Maria Sharapova, the French Open champion.
The other semi-final will see Olympic, Wimbledon and US Open winner Serena Williams facing Agnieszka Radwanska who needed three hours and 29 minutes, the longest match in the history of the 40-year-old championships, to claim a 6-7 (6/8) 7-5, 6-4 win over Italy's Sara Errani.
"It feels great, a dream come true," said Azarenka, who was also US Open runner-up in 2012 and put together a 26-match winning streak earlier this year.
"I want to play my last matches here and then enjoy being the world number one. I want to focus on this competition, there are still lots of challeges ahead."
Azarenka's achievement had looked in doubt for much of an unpredictable 68-minute first set, during which 2011 French Open champion Li hit hard, flat, and ambitiously and the favourite sometimes struggled.
After dropping her opening service game, Azarenka trailed 0-2, 1-3, and 2-4, and although she too hit some spanking ground strokes and restored parity at 4-4, she promptly dropped serve again, partly the outcome of a fourth double fault.
Li was then very unlucky not to reach set point at 5-4, 40-30, which would really have increased Azarenka's stress levels.
The Chinese player appeared to have struck a great forehand cross court winner, only for the rally to be replayed because of a line judge's incorrect call on a previous shot.
Li then lost that vital game with a double fault on break point.
The set was eventually decided by a tie-break which hinged on two points Azarenka won against the Li serve from 4-5, both from slightly over-ambitious Li over-hits.
Azarenka responded to those with a one-arm salute as triumphant as if she had actually won the match.
It had certainly taken her a fair distance towards doing so, for thereafter she played with a little more freedom advancing rapidly to 5-1.
Then tension struck again. Two games evaporated in a rush of mis-timing. When Azarenka then stood at 30-love down in the eighth game, a crisis was approaching.
She responded by hurling her racket, by threatening several times to swipe it on the court, and by picking it up and screamingly winning four points in a row.
In the end Azarenka conquered herself as well as her opponent.
Her progress ended Sharapova's outside hopes of becoming year-end world number one but could not prevent the Russian from advancing her hopes of a triumphant finish to a self-defining year.
Sharapova completed a career Grand Slam during 2012, and now she produced a table-topping third win in the White Group with an emphatic 6-0, 6-3 over 2011 US Open champion Samantha Stosur, an out-of-sorts late substitute for the unwell Petra Kvitova.
It earned a chance to avenge her Australian Open final defeat and three other losses to Azarenka this year.
"I didn't want to play as long a match as in the previous round," Sharapova said, referring to her three-hour match with Radwanska on Wednesday.
"I wanted to do a few things better and I think I did."
She may also feel that she has a less difficult task against Azarenka than she might have had facing against Williams, who has so far justified her tag as the unofficial favourite.
Indeed things are looking particularly good for the American.
Not only did the schedule enable her to conclude her third, table-topping win in the Red Group on Thursday, but she enjoyed a day's rest Friday while her prospective semi-final opponents were tearing themselves apart.
It was the Radwanska's second three-hour match in three days.
"I am exhausted," said the Pole, who lost to Williams in July's Wimbledon final.
"I have never played so many hours in three days. Now for sure it's going to be hard. No rest day.
"But I will do everything in my power to go on court tomorrow in one piece."