Swift, 27, one of the top-selling U.S. singers, wore a black jacket and white top in court as she watched the proceedings.
She is expected to take the stand during the trial in U.S. District Court to testify about the incident, which resulted in broadcaster David Mueller's firing from Colorado music station KYGO-FM.
The litigation centers on Swift's allegations that Mueller slipped his hand under her dress and grabbed her bare bottom as they posed during a meet-and-greet session before her June 2, 2013, concert in Denver.
"It was not an accident, it was completely intentional, and I have never been so sure of anything in my life," Swift said of the incident during a deposition.
Mueller, 55, sued first, claiming Swift falsely accused him of the groping and pressured station management to oust him from his $150,000-per-year job at the station, according to the lawsuit.
Swift countersued for assault and battery and that became part of the same trial.
A crowd of Swift supporters was expected to attend the proceedings.
Maya Benia, 20, a fan from Albuquerque, New Mexico, had been waiting outside the courthouse since 5:30 a.m. MDT (1130 GMT). She could not stay for the trial because of a doctor's appointment but had a letter she hoped someone would relay to the singer.
"It is a thank-you to her for consistently being there for me over the years through all my hospitalizations and also a thank for survivors of sexual assault and her being able to use her voice when others couldn't," Benia said.
Mueller denies anything inappropriate occurred during the brief backstage encounter in which he stood on one side of the pop star and his girlfriend on the other. His lawsuit said Swift's accusation is "nonsense."
Mueller is suing under tort claims of interference with contractual obligations and prospective business relations. Jurors will determine what monetary damages, if any, he is entitled to if Swift is found liable.
In court filings, Swift said her representatives informed KYGO management about the incident but she did not demand Mueller be fired.
The radio station investigated and two days after the incident fired Mueller for violating the morality clause of his contract, court documents show.
The judge has placed a gag order on all parties and attorneys for both sides did not respond to messages seeking comment.
Swift, one of the most successful contemporary music artists, earned $170 million between June 2015 and June 2016 following a world tour and her best-selling "1989" album, according to Forbes Magazine.
source: news.abs-cbn.com
