Dercksen continued her good form in the tournament, striking a career-best 81 from 80 balls while Tryon smashed 67 off 43 deliveries but the Proteas could only reach 314-7 chasing a target of 338.
There was good support from the middle-order with debutant Miane Smit, batting at number 3, scoring 39 while Nondumiso Shangase (36) and wicketkeeper Sinalo Jafta (21) made solid contributions.
Nadine de Klerk (22 not out from 13 balls), together with Tryon, kept the fight going until the final over but the Proteas ultimately fell short and were condemned to a third consecutive defeat in the tournament.
India's mammoth total was built around a century by number 5 Jemimah Rodrigues, who scored a career-best 123 off 101 balls, while Deepti Sharma blazed her way to 93 from 84 deliveries.
The Proteas bowling unit struggled in the sapping heat in Colombo and they could not restrict a rampant India outfit, with opener Smriti Mandhana laying the platform with 51.
Masabata Klaas and De Klerk took two wickets apiece while spinner Nonkululeko Mlaba also had two scalps but was expensive going for 71 in her eight overs.
The Proteas still have one match remaining in the tournament, against host nation Sri Lanka, and even though the game will be a dead-rubber in the context of the series will still want to leave on a high.
Shai Hope continued his fine form with an unbeaten century as West Indies pulled off their highest-ever T20I run-chase to beat India by six wickets and level the five-match series at 1-1.
Bhuvneshwar Kumar could be in line to make his first international appearance in four years after recalled to the India squad for the T20I series in New Zealand starting later this month.
Shreyas Iyer struck his maiden T20I century as India thrashed the West Indies by eight wickets with more than five overs to spare in the first game of the five-match series in Lucknow on Tuesday.
India captain Shubman Gill called on his side to raise their fielding standards and improve their bowling accuracy at the end of the innings after they lost the third ODI against West Indies in New Chandigarh.
