Soon after her pageant success, Krishnan began her career acting in an uncredited role as Simran's friend in Jodi before moving onto appear in advertisements and in music videos, with Falguni Pathak's Meri Chunar Ud Ud Jaye being the most prominent. The first project she accepted was the Priyadarshan-directed Lesa Lesa, with the promotional posters for the film, also creating an offer to star in the A. R. Rahman musical, Enakku 20 Unakku 18 (2003).However both the projects' releases were severely delayed, and her first release was Ameer's Mounam Pesiyadhe opposite Surya Sivakumar. The film became a moderate success at the box office and did manage to gain credentials for Trisha, with critics claiming that she was "undoubtedly a refreshing new find, with sparkling eyes and appealing demeanour", also going onto praise the dubbing artiste, Savitha Reddy, who has since regularly dubbed for Trisha. Manasellam, her second project, saw her play a cancer patient; but the film also went unnoticed despite positive reviews for the film and the actress.