The junior officer testified that Brigadier General Jeffrey Sinclair grabbed her by the back of the neck and sexually assaulted her after she tried to explain she was fed up with their adulterous affair and needed to move on.
"He pushed me down," she said through tears. "I felt like I had no control at all over my own body."
Her allegations are the basis of a forcible sodomy charge that could send the 51-year-old general to prison for life. Sinclair is also accused of grabbing her genitalia against her will and of having sex with her in public places, including a parking lot in Germany and military offices in Afghanistan.
The general, who is married, denies sexually assaulting the captain 17 years his junior and says the relationship was consensual, although inappropriate by military standards.
The rare court-martial of a high-ranking US military official is unfolding in Fort Bragg, North Carolina, amid a growing debate among US lawmakers over how best to curb sexual assault in the military.
A government prosecutor told a jury panel of five two-star generals that Sinclair abused his rank and power to threaten the captain to stay in an intimate relationship that spanned three years and two war zones.
"It involves a lot of consensual sex," the lead prosecutor, Lieutenant Colonel Robert Stelle, said during opening statements on Friday. But "this is a case where non-consensual sex was used as an instrument of control."
Defense attorney Ellen Brotman read aloud excerpts from the female captain's journal that the lawyer said help prove the liaison was based on mutual affection, not coercion, and remained consensual from beginning to end.
"You will see that this case is nothing more than a workplace affair," Brotman told jurors, adding the captain's fear was that Sinclair would never leave his wife.
The identity of the captain, a military intelligence officer, is being withheld by Reuters due to the nature of the charges.
The captain, 34, recalled on the witness stand her first physical encounter with Sinclair, saying he invited her into his private quarters in Iraq in 2009, asked her to take down her hair and caressed her face.
"I had developed a very strong attraction for him," she said. "On the one hand, I'm thinking how amazing it feels, but on the other hand, this is my brigade commander."
The captain, now stationed in Arizona, did not meet Sinclair's gaze during her testimony, during which the general sometimes shook his head and looked annoyed.
The relationship went through volatile highs and lows, and the captain said her frustration and mistrust grew. She said Sinclair once threatened, after they had sex, to kill her if she told his wife or anyone else about the affair.
Another time, at a hotel in Arizona, they had sex against her will on a balcony and Sinclair later grabbed her by the throat when she became upset and tried to leave, she testified.
After court, Sinclair's attorneys said that account contradicted her previous descriptions of the hotel meeting. In a journal entry, she wrote that they had a huge fight over a change in his travel plans but said, "It was so wonderful to be with him again though."
The captain testified that she stayed involved with Sinclair because she felt emotionally connected and worried about how ending it would affect her military career. She did not immediately report him to superior officers after the alleged sex crimes.
"I knew if I said anything that it would be my word against his and nobody would believe me," she said. "I had no way out."
When she told Sinclair of her desperation, she said he texted her, "Get a grip."
On Thursday, Sinclair, a one-star general, pleaded guilty to lesser offenses that carry a maximum penalty of 15 years in prison and possible dismissal from the Army.
He admitted to having an extramarital affair with the captain as well as asking other junior female officers for nude photos and viewing pornography while deployed.
The charges saw him stripped of command in southern Afghanistan in May 2012 and sent back to Fort Bragg, where he remains on active duty. His wife is not attending the trial.
Sinclair's attorneys said the captain's testimony provided new fodder for their cross-examination of her on Monday.
"It was an interesting story we heard," said lead defense attorney Richard Scheff. "Unfortunately, it's fiction."