The attack happened Thursday at a construction yard in Revere, The Boston Globe reported.
Carmen Scoppettuolo, 12, said he and his friend Brandon Marchetti, 14, were petting two dogs they had befriended through a fence at the construction site.
"They were actually nice," Scoppettuolo said Saturday of the two dogs, Sonny and Bella. "They only barked when we would leave, because they wanted us to stay."
However, Marchetti decided to scale the fence to get closer to the dogs, Scoppettuolo said, the Boston Herald reported.
"He felt like it was safe to hop over," Scoppettuolo said, adding at first Marchetti was petting one of the dogs. "Then someone called him. When he got off the phone, the dog started biting him."
Scoppettuolo called police, who told him to tell Marchetti to curl up into a ball and wait until police arrive.
"But they kept biting him," he said. "I wanted to throw something at them, but I didn't know if they would bite him harder."
When police showed up at the scene, officer Michael Mullen shot one of the dogs, wounding it, and other officers sprayed the dogs with a fire hose.
Marchetti was transported to a hospital where his mother, Silvana Marchetti, 47, said he remains sedated and will go into surgery on Monday.
"He was mauled badly, very badly," she said. "He will pull through, but he will need lots of plastic surgery and reconstructive surgery."
"His friend was a hero," Marchetti said of Scoppettuolo. "If it wasn't for him, my son would be dead."