Pornpawee mixed iron determination with dazzling variety to wrest control from the world No 5 with a 15-21 21-11 21-18 victory.
“My hands and legs felt tight in the first game because I was so excited to be in my first Tour Finals,” said the 23-year-old, third in national rankings topped by Ratchanok. “But then I refocused and tried to make her play my game. I ran down all shots in the third game while she seemed to be under serious pressure,” added the 2020 Spain Masters winner.
In another group B see-saw battle, world No 1 Tai Tzu Ying of Taiwan rallied after losing the first game to beat the 2018 champion PV Sindhu of India 19-21 21-12 21-17.
“I had the lead early in the first game but then I started to rush things and that led to the unforced errors,” said Tai, who was beaten two weeks in a row by Spain’s Carolina Marin on her way to both Thailand Open titles earlier this month.
“I have played two tournaments [this month] now and it's very tiring. It was difficult to focus on court today,” said Tai, runner-up at the 2019 World Tour Finals to Chen Yufei of China.
In group A, Marin of Spain continued her dominant form with a convincing 21-19 21-14 win over Evgeniya Kosetskaya of Russia.
The former world No 1 proved superior in all aspects to beat the first Russian to reach the season finale.
“The first game was tough after winning back-to-back titles,” said Spain’s 27-year-old world No 6. “It's tough to be [mentally] ready again for a new week, a new match and a new tournament, but I managed to win today and will now prepare for tomorrow,” added Marin, who has not dropped a game in her last 11 matches.
Also victorious in the group was South Korea’s rising star An Se-young, who toppled Michelle Li of Canada 21-12 21-17.
On the men’s side, Taiwan’s world No 2 Chou Tien Chen needed three games in group A to beat Lee Zii Jia of Malaysia, 21-16 12-21 21-11. In group B, world No 3 Anders Antonsen of Denmark benefited from a barrage of errors by Srikanth Kidambi of India to prevail 15-21 21-16 21-18. Fourth-seeded Wang Tzu Wei of Taiwan ousted Ng Ka Long Angus of Hong Kong 21-10 21-14.
In mixed doubles, Thai hopes Dechapol Puavaranukroh and Sapsiree Taerattanachai rode red-hot form as Thailand Open I and II champions to beat Praveen Jordan and Melati Daeva Oktavianti of Indonesia 21-13 16-21 21-11 in group A.
In women’s doubles, Thailand’s Jongkolphan Kititharakul and Rawinda Prajongjai upset fourth-seeded Chloe Burch and Lauren Smith of England 21-10 21-11 in group B action.