A man was stabbed on a Manhattan train while defending himself from a would-be robber — less than a half-hour before a good Samaritan was slashed at another station as he tried to help a woman who was being attacked, cops said Wednesday.

The first of the back-to-back transit assaults took place around 10 p.m. Tuesday after a 34-year-old man got into it with a stranger who tried to steal money from him on an F train near the 34th Street-Herald Square station.

Then at around 10:25 p.m., a 28-year-old woman was slashed in the face at the Union Square station by a creep who then attacked a man who jumped in to defend her.

All three victims were expected to survive.

The man injured in the first incident had been riding a southbound train when the stranger approached, asked for a cigarette and then tried to rob him, authorities said.

As the two men fought, the suspect pulled out a knife and stabbed the victim twice in the stomach. When the train pulled into the station, the tussle spilled onto the platform, where the attacker stabbed the man again before taking off, authorities said. 

The victim was taken to Bellevue Hospital with non-life-threatening injuries, cops said.  Nothing was stolen.

Just 25 minutes later, the other harrowing attack broke out on the L train platform at Union Square, when the separate suspect slashed the woman during a dispute, cops said. It’s unclear what the fight was about.

A 29-year-old man who wasn’t involved in the dispute tried to step in to grab the attacker – who then turned on him, slashing him several times on the head, authorities said. 

The attack left a gruesome scene for fellow commuters as blood spotted the platform and upper mezzanine.

Both the man and woman were taken to Bellevue Hospital in stable condition.

Outside the station, a man with a bandage wrapped around his head and a blood-drenched shirt was wheeled into an ambulance.

The suspect fled the station in an unknown direction. No arrests had been made by Wednesday morning.