An unhinged attacker slashed a man and a woman in back-to-back knife attacks inside Grand Central Station, police said Wednesday. The first victim, a 42-year-old man, got into a quarrel with the attacker on the uptown No. 4, 5 and 6 platform at the Grand Central-42nd St. subway stop about 10:10 p.m. Tuesday, cops said. As the Christmas Eve spat escalated, the assailant slashed the victim’s wrist and ran off. The stabber fled up a flight of stairs where he proceeded to pick a fight with a 26-year-old woman before slashing her neck inside the station, cops said. Medics took both victims to Bellevue Hospital in stable condition. Police apprehended a 28-year-old man after the second stabbing. Charges against him are pending. A knife was recovered at the scene.