Sri Lanka produced an impressive run chase to down India by six wickets on Tuesday and leave their opponents staring at an early exit from the Asia Cup.
If Pakistan beat Afghanistan on Wednesday, they will face Sri Lanka in Sunday's final and knock out arch rivals India in the process.
Half-centuries from openers Pathum Nissanka (52) and Kusal Mendis (57) gave Sri Lanka the perfect start to their chase of 174 in the Super Four game of a tournament which acts as a tune-up to the T20 World Cup in October-November.
India hit back with a flurry of wickets, but Bhanuka Rajapaksa and captain Dasun Shanaka, who hit an unbeaten 33, helped Sri Lanka get over the line, with two scrambled byes off the penultimate ball completing the job.
"The environment in the team set the tone. It is what gave us the confidence," said man of the match Shanaka, whose team began the tournament with a heavy defeat against Afghanistan but bounced back with three successive wins.
"The batting unit won it for us. The bowlers bowled well in patches, Dilshan and Theekshana in particular. The Indian batsmen came hard, but we did well to keep them to 173."
Rajapaksa, who hit 25 not out, and Shanaka put on an unbeaten stand of 64 to leave the hopes of tournament favourites India hanging by a thread, after also losing their Super Four opener to Pakistan.
Left-arm quick Dilshan Madushanka led the bowling charge with figures of 3-24 in his four overs to keep down India to 173-8 despite a 41-ball 72 from skipper Rohit Sharma.
If Afghanistan do India a favour against Pakistan, Rohit's men will still have to beat the Afghans on Thursday to have any chance of reaching the final.
'LOOKING FOR ANSWERS'
Nissanka started cautiously before he hammered Arshdeep Singh for two fours and a six in an 18-run fifth over.
Mendis joined in the fun and cleared the fence three times, including with a brilliant shot over wide long-off against Ravichandran Ashwin.
Nissanka reached his fifty in 33 balls, but Indian legspinner Yuzvendra Chahal broke the partnership and struck twice in one over.
Mendis also completed his fifty but Sri Lanka lost Danushka Gunathilaka for one off Ashwin.
Chahal then trapped Mendis lbw to put Sri Lanka in trouble at 110-4 from 14 overs.
But Rajapaksa and Shanaka dug them out of that hole with some inspired batting, leaving only seven needed from the final over.
With two still to get from two balls, Shanaka played and missed outside off stump, but wicketkeeper Rishabh Pant and bowler Arshdeep both failed with their run out attempts and the match finished on an overthrow.
"Since the last World Cup (when India failed to make the semifinals), we haven't lost much," said Rohit.
"We wanted to put ourselves under pressure during this Asia Cup. We are still looking for some answers."
Rohit put on 97 with Suryakumar Yadav (34) after India lost two early wickets including Virat Kohli for nought.
Kohli, who struck form after an extended batting slump with two successive half-centuries in the tournament, walked back to stunned silence from a sparse crowd dominated by Indian fans.
Rohit hit back with a flurry of boundaries but his departure opened the door for Sri Lanka who took late wickets to keep the score down.
Shanaka returned figures of 2-26 with the key wickets of Suryakumar and Hardik Pandya in his two overs. Chamika Karunaratne also took two wickets.
INDIA: KL Rahul, Rohit Sharma (capt), Virat Kohli, Suryakumar Yadav, Rishabh Pant (wk), Deepak Hooda, Hardik Pandya, Bhuvneshwar Kumar, Ravichandran Ashwin, Yuzvendra Chahal, Arshdeep Singh
SRI LANKA: Danushka Gunathilaka, Pathum Nissanka, Kusal Mendis (wk), Charith Asalanka, Bhanuka Rajapaksa, Dasun Shanaka (capt), Wanindu Hasaranga, Chamika Karunaratne, Maheesh Theekshana, Asitha Fernando, Dilshan Madushanka