One homeless man slashed another in the chest at a Midtown shelter on Saturday, only three days after a homeless man was slashed to death and nearly decapitated at another shelter in East Harlem.

The 11 a.m. attack came just two hours after Mayor Bill de Blasio held a press conference announcing he’s beefing up security at the city’s notoriously dangerous shelters.

Mark Bradford, 48, was smoking in a room at the 53rd Street Men’s Shelter between Second and Third Avenues when a 36-year-old fellow resident told him to stop, cops said.

Bradford allegedly slashed the rival in the chest inside a shelter elevator an hour later. Police did not reveal the victim’s condition.

Cops arrested Bradford at 12:15 p.m. at Lexington Avenue and East 53rd Street; he’s charged with assault.

Bradford has some 30 arrests on his rap sheet, cops said. The latest, in August, was for allegedly selling a fare card. Cops also found him in possession of several bent MetroCards, allegedly used to swipe into the subway for free.