A knife-wielding woman slashed another female commuter as tensions flared during the Thursday morning commute in downtown Brooklyn — and then turned herself in a short time later, cops said.

The victim, 44, had just gotten off an R train at the Jay Street-MetroTech station around 9:40 a.m. when she and Jahlayah Blondel, 26, got into a heated argument, according to authorities and sources. 

The clash turned violent when Blondel — a stranger to the victim — allegedly pulled out the blade and cut her on the left shoulder, police said. 

The victim was taken to NYU Langone Health—Cobble Hill with minor injuries, cops said. 

Blondel, of Staten Island, initially fled the scene and ditched the knife, police said. 

But she then turned herself in around 10:10 a.m. at the NYPD’s Transit District 30 headquarters, located inside the Hoyt/Schermerhorn Street station, police said. 

She was charged with assault, criminal possession of a weapon and tampering with evidence, cops said. 

The alleged slasher has no previous arrests in the Big Apple, police said. 

The attack came just over 12 hours after a 17-year-old boy was slashed with a box cutter inside a Harlem subway station, cops said. 

The victim was cut on his left wrist around 9:25 p.m. Wednesday during a feud with two teen boys and two teen girls on the B and C train platform at West 135th Street, according to authorities. 

He was taken to Harlem Hospital, where he is listed in stable condition. 

The young suspects fled the scene and remain at large.