A 26-year-old homeless man fatally stabbed inside a Hell’s Kitchen apartment left a gory blood trail from the third floor all the way to the front stoop as he slowly bled out from a gaping stomach wound, police and witnesses said Friday.

Victim John Carlos Mesa was found “covered in blood” when a tenant from the W. 47th St. apartment building near 9th Ave. saw him outside the building on his cellphone moments after the Wednesday afternoon stabbing.

“I saw (him) stumble out of the building and down the stoop,” said a 25-year-old tenant, who didn’t wish to be named. “He was on the phone, and he just seemed like he was talking with a friend. He wasn’t insanely screaming for help or anything.”

As the woman drew closer, she could clearly see his shirt was soaked with blood.

“He was holding his stomach,” she said. “He put his hand up by his head, and that’s when I saw that clearly there was, like, an injury to his stomach. He was definitely losing a lot of blood. He was swaying back and forth.”

Grisly details about the 2:45 p.m. stabbing came out as cops charged a third-floor tenant of the building, Carlos Andres Delgado Lopez, with murder for killing Mesa and attempted murder for stabbing a 35-year-old woman also inside the apartment.

Delgado Lopez, 31, knew both of his victims, police sources with knowledge of the case said. It wasn’t immediately clear what sparked the stabbing.

A second tenant, Jorge Bender, told WABC Eyewitness News that he helped put pressure on Mesa’s wound and called 911 for him.

“From the size of the wound – and I could see some of the tissue hanging out. I suspect it’s a stabbing,” Bender said Thursday. “I (told the 911 operator), ‘The gentleman is distraught, he’s very pale.’ I said, ‘He only speaks Spanish and some English. Just please send an ambulance.’”

The woman who found Mesa outside the apartment immediately ran into her building, only to find a sickening blood trail leading from the lobby to a blood-soaked elevator.

She opted to take the stairs to the third floor, only to learn that the stabbing had occurred next door to her apartment.

“I noted the blood trailing practically to my apartment, and that’s when I freaked out because my roommate was home. I was like, ‘Is she okay?’”

After she called 911 and alerted the building’s super, her roommate told her that she had heard Mesa screaming in the hallway after the stabbing.

“Call the authorities! Call the authorities!” Mesa screamed as he ran down the hall. “Someone’s trying to kill me!”

Medics rushed both victims to Mount Sinai Morningside Hospital, where Mesa died. The wounded woman was expected to survive.

Neither Delgado Lopez nor his two victims have criminal records, police said.

The third-floor tenant said that another man and a woman lived with Delgado Lopez, but it wasn’t immediately clear if they were the two stabbing victims.

After searching, cops couldn’t find an address for Mesa, an NYPD spokesman said.

She said she would say hello to them in passing, “but that was it.”

“The woman was always dressed to the nines,” she said. “I was honestly very confused where she was going all the time because she was dressed up so nice where I was, like, ‘Dang, like we have a fashionable neighbor!’ She’d always be in heels and like a dress. Full face of makeup.”

The three who lived in the apartment spoke Spanish and were pretty loud, she remembered.

“They were pretty loud neighbors,” she said. “But it was nothing of like concern.”

Delgado Lopez’ arraignment in Manhattan criminal court was pending Friday morning.