Azarenka won 7-6(4) 6-3, but it was an error-strewn match that she almost won by default. The good news is that the Belarusian confirms her end of year ranking as world number one, whatever happens next, becoming the 11th player to do so since the WTA began its rankings in 1975.
"It's kind of difficult to believe that a little girl from Belarus is on that list," the 23-year-old said. "But it's really an incredible achievement.
"When I started to play tennis I had this big picture in my head that I want to be there. Back then it was so far away. It was like pretty much touching the sky," added Azarenka.
She will face world number two Maria Sharapova for a place in the final after the Russian easily ousted Sam Stosur 6-0 6-3 to win the White Group, while Radwanska’s three hour 29 minute victory over Sara Errani - the longest ever match played at a WTA Championships - put her into a semi-final against Red Group winner Serena Williams.
The results also mean that the top four make up the semi-finals, justifying their rankings at this stage, although world number three Williams remains favourite for the title.
Li, who was dreadful in her opening defeat to Williams but improved in beating Angelique Kerber, started well with a fine break, unleashing some rasping baseline bullets as the world number one began sloppily.
But Azarenka, who has not been at her best at these Championships, twice came from a break down, including breaking back while the notoriously flaky Li served for the first set, before taking a scrappy tie-break as the Chinese threw in a couple of double faults to help her along.
The Chinese number one’s malaise continued as she allowed herself to be broken at the start of the second, a dreadful miss handing the game to the prone Azarenka. But the 23-year-old from Minsk was far from convincing herself, and was broken back at the first time of asking as her predictable shots were met with interest.
It was a grind, heavy on the eyes in comparison to the earlier match between Radwanska and Errani, with Azarenka gifted a second break of the set by some awful serves and follow-ups from Li.
Azarenka was able to up her level though, holding to love before breaking again as Li double-faulted for the seventh time. The Australian Open champion was now two breaks to the good and despite the occasional fine point and a shocking Azarenka self-break while serving for the match, there was no way back for Li, who was broken again and exits with a 1-2 record.
That match started close to 10.30pm local time after Radwanska fought through with an epic 6-7(6) 7-5 6-4 win over Italy’s Errani.
With Sharapova comfortably through as White Group winner after a straightforward triumph over the already-out Stosur, it was a straight shootout between two stylish counterpunchers for a spot against Williams in the last four.
It turned into an almighty battle of wills and skills, with Radwanska justifying her higher ranking by coming from behind to oust the 25-year-old.
“I need a lot of treatment just to make (the next) match,” world number four Radwanska told Eurosport on court afterwards.
“I have played a lot of tennis these last three days and it’s tough to play these kind of matches. I’ll do my best and we’ll see. I have nothing to lose.”
And an entertaining clash it was, lasting three-and-a-half hours as both women displayed a wonderful array of technical shots, fantastic speed and movement – and remarkable power for two of the smaller women in the top 10.
Errani shaded the first set on a tie-breaker as the Italian showed superb composure on her drop shots in particular, while Radwanska initially struggled to shrug off Thursday’s three-hour opus against Sharapova.
But a topsy-turvy second set, in which both women broke seemingly at will, went the way of the Krakow-based 23-year-old as her opponent seemed to fade, getting her previously effective drop shots all wrong as the world number four bullied her from the baseline before breaking in the final game.
Errani, who at one point was a Radwanska service game away from victory, seemed to collapse, losing 12 points and five games in a row to fall 0-3 in the third, despite playing her part in some fantastic rallies that involved a full repertoire of shots and movement from both women.
That did for the world number seven as, while the petite Italian did manage to break back a few times including when Radwanska was serving for the match, the Pole’s two-game advantage was just too much for her in the end as she fought to a vital hold to claim victory, Errani returning long to finish things off just short of the 210-minute mark.
"She's a big fighter so she didn't give up," Radwanska said. "So I really had to play my best tennis until the end of the match."
Sharapova’s victory was ruthless and simple as she cruised to a 6-0 6-3 win over Stosur.
In what was effectively a dead rubber – Sharapova had already qualified for the knockout stage, while Stosur had no chance of progression – the Russian blitzed her opponent in the first set as the sub-par Australian totally flopped, winning just five points as she slumped to a bagel.
It was embarrassing at times. Stosur was a late entrant to the finals after an ill Petra Kvitova withdrew following her first match, and after capitulating against Errani on Thursday, the world number nine looked like she wanted to return to her holidays.
The second set was more competitive, Stosur almost breaking Sharapova on a couple of occasions as she found some fight and power in her backhands in particular.
But Sharapova had her eye on the $115,000 match winner’s prize, regained her composure on serve, and broke late on to complete the victory in just over an hour.
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- Maria Sharapova
- Sara Errani