To the roaring approval of the fiercely partisan home crowd, Busanan crushed Li — who was returning from injury — 21-11, 21-9, setting up a showdown on Saturday against top seeds Japan.
Earlier Japan brushed off a challenge by South Korea 3-1.
But the day belonged to the Thais, whose win sparked jubilant on court celebrations and ended a see-sawing match up with tournament favourites China.
World Number 4 Ratchanok Intanon won the first singles game, grinding out a 15-21, 21-9, 21-14 win over China’s Chen Yufei, who is ranked one place behind her.
With crowds shouting “Thailand! Thailand!” Ratchanok hit smash after smash to come back after losing the first game to win two in a row.
“I was a bit excited because every point was important, especially in the final rounds,” she told reporters afterwards.
“I thank the Thai sport fans that come to support.”
Thailand lost the first doubles, but singles shuttler Nitchaon Jindapol clawed her way back from a set down to beat Gao Fangjie in another thriller that had the crowd on their feet.
The second doubles went to China levelling up at 2-2, leaving Thai hopes on Busanan, just as they did on Thursday when she performed under pressure to clinch a victory against Indonesia.
On Saturday the Thais now face top-seeded Japan.
They beat South Korea in their semi, with doubles pair Misaki Matsutomo and Ayaka Takahashi securing their spot in the final.
World number two Akane Yamaguchi got the team off to a flying start, easing to a 21-10, 21-13 win against South Korea’s Sung Ji-hyun, while Nozomi Okuhara dispatched Lee Jang-mi 21-9, 21-15.
South Korea had levelled at 1-1 with the first doubles pairing but Matsutomo and Takahashi settled the tie.
Japanese world number nine Okuhara has yet to lose in this year’s biennial Uber cup, which is being held in Bangkok.
“I think it will be a tough battle whoever I face tomorrow,” she told reporters afterwards.
The tournament is held alongside the men’s Thomas Cup, whose semi-finals are being held later Friday, with China, Japan, Indonesia and Denmark all hoping to move forward.
Denmark are returning champions, and are back to attempt a repeat with world number one Viktor Axelsen leading the team.
But China have fielded an all-star cast of players as they seek to regain a title lost on home soil two years ago.
Olympic champion Chen Long is joined by this year’s All England champion Shi Yuqui — and the player he conquered in the final, Lin Dan.