A driver flagged down police in the South End after three men allegedly robbed him at knifepoint.

According to police, officers arrested Joey Sierra, 22, of Boston and Edgar Matos, 22, of Boston and charged them with armed robbery after they allegedly stole a cell phone, necklace and Cincinnati Reds hat from a man sitting in his parked car.

Just before 1:30 a.m., three males approached the victim in his vehicle on Harrison Archways, police said.

According to the victim, one of the suspects displayed a knife and demanded the items before fleeing the area with the goods.

The victim contacted police and were able to locate two of the suspects.

Police said Sierra, who did not run, was wearing a Cincinnati Reds baseball hat that he allegedly just stole.

While officers were talking to Sierra, witnesses were brought to the scene.

Upon seeing the suspect, witnesses stated, “that’s one of them,” police said.

The third suspect was not caught, according to police reports.