The trial against Kevin Tully, 25, who is accused of stabbing Elroy Bitt, began Monday in district court in Aztec.
Tully is charged with attempted first-degree murder and aggravated battery.
Mark Curnutt, Tully's attorney, said his client was acting in self-defense.
Tully was a member of the U.S. Army National Guard and was wearing his army fatigues when police said he attacked Bitt with a utility knife on Sept. 2, 2011.
Bitt had stab wounds to his stomach, neck, arm and the back of his head. His lung was punctured during the attack, according to court documents.
In court on Monday, jurors heard from several police officers who investigated the case, the doctor who treated Bitt in the emergency room, a recorded conversation between Tully and Farmington Police detectives and Andrea Talk, Tully's ex-girlfriend.
Tully and Talk had been in an 11-year relationship and had two young children together. They shared an apartment in Farmington until the couple broke up days before the attack, Talk said in court.
Police said Tully was in Santa Fe completing Army training when he got into an argument with Talk on the phone the night of the attack.
On the night of the stabbing, Talk was with friends at the B Lounge in Farmington. Tully called her repeatedly from different phone numbers throughout the night, Talk said in court.
Tully told Farmington police that while on the phone with Talk, he heard a man say, "You take care of your country, I'll take care of your wife," according to a taped recording of the conversation played in court.
Tully then had a friend, Pfc. Esteban Villa, drive him from Santa Fe to Farmington, where Tully arrived around 2 a.m. on Sept. 2.
Talk said Tully climbed through a window and entered the apartment where he attacked Bitt about 2:30 a.m.
"He had blood on his uniform," Talk said of Tully. "He was calling me names."
Tully's attorney, Curnutt, questioned Talk about how much she was drinking the night of the attack. He pointed out that Bitt was a "complete stranger" to her and she didn't know his name when she reported the stabbing to police.
"Did you consider (Tully) was calling because he was concerned about you or his kids?" Curnutt said.
Tully turned himself into police about 30 minutes after the stabbing and gave them the utility knife. He admitted to stabbing Bitt during his interview with police, but said he was acting in self-defense.
Bitt is expected to testify in court Tuesday and Tully also could testify.