A Pomona Superior Court jury on Thursday convicted Gabriel Andrew Ojeda and Mark Antoine Hachem of assault by means likely to produce great bodily injury, said Los Angeles County district attorney's spokeswoman Jane Robison.
Ojeda additionally was convicted of a count of misdemeanor assault, and Hachem was convicted of a count of intimidating a witness, Robison said.
The jury acquitted Ojeda of a witness intimidation charge.
Glendora police suspected the attack was carried out because the victim, a 22-year-old man, was a potential witness in an unrelated assault case, authorities said in the days following the arrest.
Ojeda immediately received a sentence of four years and six months in state prison, officials said.
Hachem was ordered to return to court for sentencing on Thursday.
The beating took place Dec. 26 at Gladstone Street and Willow Avenue in Glendora.
The assailants continued punching and kicking the victim even after he was knocked to the ground, resulting in serious injuries including a broken jaw, police said.