(CNN) -- Defending champion Serena Williams overcame a gutsy display from Jelena Jankovic on Saturday to reach the final of the WTA Championships in Istanbul. 

The World No.1 was forced to work hard against her Serbian opponent in the Sinan Erdem Dome, but eventually came through to win in three sets 6-4, 2-6, 6-4 to set up a showdown with China's Li Na in Sunday's final. 

Williams started slowly and was soon 3-1 down but fought back to take the opening set. But any thoughts of a quick finish were dashed as errors crept into the American's game. Jankovic took full advantage winning the set with ease. 

A more composed Serena returned in the deciding set which she won 6-4 but not before Jankovic had gamely saved three match points. 

"I'm just really trying out here. I think my body's a little tired after so many matches -- I think yesterday I kind of hit a wall. But I'm just fighting out here," Williams said. 

"Honestly I'm just happy to still be in the tournament, and I'm honoured to be in the final again." 

Li's match against Petra Kvitova was a less exhausting affair with the 31-year-old seeing off the Czech left-hander 6-4, 6-2. 

Li had already broken new ground by becoming the first Chinese woman to reach the semifinals of the WTA Championships, but by beating Kvitova, she has risen to World No.3 and becomes the highest ranked Asian women in history. 

With both Li and Williams undefeated in the tournament so far, the winner of Sunday's match will walk away with Â£2,145,000 while the runner-up is guaranteed $1,090,000. 
Who was the defending champion?
What competetion was she in?
Where was it?
Who did she play?
Did she win?
In how many sets?
Where is Dome from?
How did Williams body feel?
What did she say it felt like she had hit?
How did Williams feel about being in the finals?
Who did Li play?
How old is Li?
Where was her opponent from?
Is she right handed?
What was Li the first to be?
What is she ranked now?
Did Li & Williams suffer losses?
How much will the winner get?
And the runner up?
When will the match be?
Serena Williams
Defending champion Serena Williams
WTA Championships
to reach the final of the WTA Championships
Istanbul
the WTA Championships in Istanbul
Jelena Jankovic
 overcame a gutsy display from Jelena Jankovic
yes
 to reach the final of the WTA Championships in Istanbul
three
to win in three sets
her Serbian opponent in the Sinan Erdem Dome
 her Serbian opponent in the Sinan Erdem Dome
tired
 I think my body's a little tired
a wall
 I think yesterday I kind of hit a wall. But I'm just fighting out here," Williams said. 

honoured
Honestly I'm just happy to still be in the tournament, and I'm honoured to be in the final again.
Petra Kvitova
Li's match against Petra Kvitova 
31
 the 31-year-old seeing off the Czech left-hander 6-4, 6-2. 
Czech Republic
the Czech left-hander 6-4, 6-2. 
no
 the Czech left-hander 6-4, 6-2. 
first Chinese woman to reach the semifinals of the WTA Championships
becoming the first Chinese woman to reach the semifinals of the WTA Championships
World No.3
she has risen to World No.3 
no
With both Li and Williams undefeated
Â£2,145,000
the winner of Sunday's match will walk away with Â£2,145,000
$1,090,000
the runner-up is guaranteed $1,090,000
Sunday
the winner of Sunday's match