A New York diamond dealer pleaded guilty on Thursday to stealing more than $400,000 worth of diamonds from two sellers and replacing them with cheaper lab-grown stones in a scheme he operated out of a Manhattan storefront.

The dealer, Manashe Sezanayev, 41, who owned Rachel’s Diamonds, a jewelry store in the heart of the borough’s diamond district, admitted to taking three diamonds he claimed to be interested in buying and surreptitiously swapping them with counterfeit versions while the sellers weren’t looking.

Mr. Sezanayev was indicted in Manhattan criminal court in July on charges of grand larceny, scheming to defraud and criminally possessing a forged instrument for his role in the scheme.

He pleaded guilty to grand larceny, which is a felony, and is expected to receive five years of probation and no prison time, according to the Manhattan district attorney’s office. Mr. Sezanayev has paid $200,000 in restitution and returned one of the stolen diamonds to the victim, the office said.

Alvin L. Bragg, the Manhattan district attorney, said in a statement on Friday that Mr. Sezanayev was now facing accountability for his crimes.

“We will continue to prosecute those who take advantage of consumers and conduct business deals in a dishonest manner,” Mr. Bragg said.