Now that’s one generous tip.

A regular diner at a Long Island restaurant donated her kidney to the ailing manager of the popular Italian eatery, officials said.

Susanne Deegan, 55, offered the life-saving donation to her buddy David Geliashvili on the spot when he first told her and her family that he was suffering from polycystic kidney disease when they visited La Bussola in Glen Cove.

“I didn’t need to think about it,” Deegan said in a statement provided by Northwell’s North Shore University Hospital. “When he told us he was sick and needed a kidney, I said, ‘I’ll get tested.'”

She was so moved by Geliashvili, 51, that she decided to get tested — and to everyone’s surprise — turned out to be a match months later, officials said.

Surgeons Elliot Grodstein and Aaron Winnick performed the transplant March 10 at North Shore University Hospital in Manhasset, a Northwell spokesperson said.

For Geliashvili, the surgery was the culmination of a 16-month process with Deegan.

Now, the single dad from Locust Valley said in a statement he is now off dialysis with a fresh outlook on life.

“I have a fighter’s instinct,” said Geliashvili, who has worked two jobs even while sick since emigrating from the former Soviet republic of Georgia in 1999.

“She’s my angel!” he added of the donor.

Northwell, which recently launched a new ambassador program aimed at driving up living organ donations, said that Geliashvili and Deegan’s story is exactly the kind of example it hopes to inspire more people to get tested for donations.

The ambassador program has driven a 25% increase in living organ donations since launching three years ago — but more than 700 patients are currently on Northwell’s transplant wait list hoping for a lifeline.

“It happened in the most Long Island way possible — a scene straight out of an Italian restaurant,” a spokesperson for Northwell said.