The women were investigating misplaced items in their back yard early Friday morning when the man attacked.
The seemly random and unprompted attack occurred just before 6:00 a.m. on Longview Road.
According to the investigation, the women noticed several items from their shed strewn around the back yard.
When the women went into the yard to investigate and approached the shed, police said Morgan Mesz, 25, of Union Township emerged and stabbed both women several times.
A neighbor, Hernan Agudelo, 33, came to the women's rescue. He jumped a fence after hearing the women scream and hit Mesz in the head with a baseball bat, ending the attacks. Agudelo suffered several stab wounds during the altercation.
"He put himself in danger, actually, but I guess he was sure that he would tackle him down," neighbor Alex Kepuladze said. "But if he didn't help, he would've killed the women. I don't know. I don't know what would have happened...It's scary, very scary."
Agudelo received treatment at a local hospital and was later released.
"This act of selflessness and bravery is commendable," said Prosecutor Theodore J. Romankow. "Without Mr. Agudelo's brave actions this situation could have been much worse."
The victims were taken to University Hospital in Newark. The first, a 53-year-old woman was listed in critical condition. The second, 50-year-old woman underwent surgery for her wounds Friday afternoon.
Mesz was charged with three counts of attempted murder and was being held on $1.5 million bail.
Mesz would be undergoing a psychological evaluation, authorities said.
Township authorities and the prosecutor's office were investigating the matter and awaiting results of a toxicology test.