The fifth-seeded Sindhu held her nerve and dug deep to edge the second seed Tai Tzu Ying in a gallant 12-21, 23-21, 21-19 comeback win that took 1 hour 11 minutes to complete.
The win assured her of her fifth medal from this prestigious tournament and helped her emulate the feat of the legendary Zhang Nin as the second player to win five medals from the World Championships. Sindhu had earlier won a couple of bronze medals in 2013 and 2014 and backed it up with a couple of silver medals in 2017 and 2018.
Sai Praneeth, meanwhile, continued to be the giant-killer at this prestigious Grade 1 tournament. A day after stunning the World No. 8 Anthony Sinisuka Ginting, Sai knocked out the in-form World No. 4 Jonatan Christie 24-22, 21-14 in 51 minutes.
Sai's achievement is even more significant for he not only secured his first-ever medal from the World Championships but also sealed India's first men's medal 36 years after the badminton icon Prakash Padukone won a bronze in 1983.
Sai will next cross swords with the top seed and World No. 1 Kento Momota in a tough semi-final showdown on Saturday.
The 16th seed arrived at this tournament in a rich vein of form. Having reached the final of the Swiss Open in February, he made it to the quarters at the India Open and the Thailand Open and the semis at the Japan Open. This week, he has looked determined to carry that form into all the three matches he has played and is yet to drop a game.
Sindhu, who had a shabby 4-10 head-to-head record against Tai, had incidentally beaten the Chinese Taipei shuttler in their last face-off at the BWF World Tour Finals in December. However, a repeat of that win did not look likely when the quarter-final clash commenced today.
Tai brought forth her array of soft touches and wily deception to throw Sindhu off her perch. She looked in control of proceedings as validated by the 21-12 scoreline in the opening game.
Sindhu settled into the match in the second game and found her aggressive shots to blunt Tai's game. Staying on the heels of the former World No. 1, the fifth-ranked shuttler managed to inch ahead at 20-18 to pocket two game points.
A resilient Tai came storming back to level the game before Sindhu made one last push to force a decider.
Even in the third game, the early momentum was with the second seed who was ahead till 14-12. However, Sindhu found her fiery smashes right on time to equal the scores at 17-17 and she was then helped by Tai's errors to go up 19-17. Once more the higher-ranked player evened up the score only to see a cautious Sindhu cross the finish line.
The Indonesia Open runner-up will next take on the winner of the quarter-final between the All England Open champion Chen Yufei and 12th seed Mia Blichfeldt.