Navor Millan made the plea for two charges including man–slaughter and use of a deadly weapon to commit a felony.
In exchange for the plea, a second degree murder charge was reduced.
Millan will appear for sentencing in Dawson County District Court on August 18.
Police say Millan stabbed Matzar several times. Then, Millan called an ambulance.
When police arrived, he informed investigators of the stabbing.