Serena regained her composure after smashing her racquet and being on the brink of defeat to beat Wozniacki 2-6, 6-3, 7-6 (6) and reach the title match at the WTA Finals.
Under the rules of the round-robin competition, Ivanovic needed to win in straight sets to leapfrog Serena in the group standings and snatch the last available semi-final spot.
"I believe in myself and I believe in my skills. I've been playing well, so I believed I could beat anyone," said the 24-year-old.
Sharapova record her first victory at this year's WTA Finals with a 7-5, 6-7(4), 6-2 triumph over Radwanksa but the Russian still bowed out of the elite tournament.
Serena Williams rebounded from the worst beating of her professional career to rout Eugenie Bouchard 6-1, 6-1 at the WTA Finals on Thursday.
The Indo-Zimbabwe pair were made to work hard by the US duo of Raquel and Abigail as they won the match in super tie-break 6-3, 2-6, 12-10.
Kvitova beat Maria Sharapova 6-3, 6-2 at the WTA Finals on Thursday and ended the Russian player's hopes of claiming the year-end No. 1 ranking.
Wozniacki moved closer to a place in the semi-finals at the WTA Finals by beating Radwanska 7-5, 6-3 on Thursday.
Ivanovic recovered from her opening loss to race to a 6-1, 6-3 victory over an out-of-sorts Bouchard on Wednesday.
Serena Williams suffered one of the heaviest defeats of her long and illustrious career as she was humbled 6-0, 6-2 by Halep at the WTA Finals on Wednesday.
Wozniacki won 7-6 (4), 6-7 (5), 6-2 to beat Sharapova for the second-straight time, having also won in the fourth round of the US Open.
The three-time defending champion made it 16-straight wins at the season-ending championships by beating Ana Ivanovic 6-4, 6-4.
Samantha Stosur continued her love affair with the Osaka hardcourts by claiming a third Japan Open title after edging Zarina Diyas of Kazakhstan in Sunday's final.
Williams is the first player to qualify for the year-ending WTA Finals to be held in Singapore from October 17-26.