A Miami police officer who wore a wire for the FBI to root out corruption in his own department pleaded guilty Wednesday to an extortion charge for providing protection for a Liberty City sports-gambling ring.

Nathaniel Dauphin, 41, admitted he received between $4,000 and $5,000 from the owner of the sports-betting business from November 2010 until March of last year. Unbeknownst to him, Miami-Dade Police detectives had the place under surveillance, witnessing Dauphin as he took money from the owner of the Player’s Choice, a barber shop that fronted for the illicit sports-betting business.

“During these conversations, law enforcement observed Dauphin take receipt of a cash payment,” according to a statement of facts filed with his plea before U.S. District Judge Marcia Cooke. “Video footage and still photos were taken.”

Dauphin, a police officer since 1996, faces up to 20 years in prison, but he is expected to receive a substantial sentence reduction for his assistance in the federal corruption probe.

Last March, Miami-Dade police shut down the gambling establishment at 6301 NW Sixth Ave., arresting the owner and four associates on state charges. That is when the FBI and Miami police internal affairs unit launched their corruption investigation, flipping Dauphin to help target other city cops.

When FBI agents interviewed Dauphin, he admitted he had agreed to provide security for the gambling operation, which took bets on local and out-of-state football and basketball games, according to the statement. Dauphin also admitted he was paid about $400 a week for protecting the gambling establishment on weekend nights from being robbed or getting caught for breaking the law.

Soon after, Dauphin began cooperating with the feds.

At the direction of FBI agents, he met with fellow Officer Harold James in early April and paid him $100 for providing “protection coverage” at the betting operation, according to court documents and sources familiar with the case. Then, while secretly recording their meeting, Dauphin enticed James to provide protection for another business that was purportedly cashing fraudulent tax refund checks.

The “cat is doing something shady ... trying to keep from getting hit,” Dauphin told James, referring to the check-cashing proprietor. Dauphin told James he would be paid “cash under the table.”

James’ response: “Sounds good to me.”

James, while under surveillance by the FBI and Miami police internal affairs detectives, provided protection for the Liberty City check-cashing store — in reality, part of an undercover FBI “sting” — five times in April and May 2012, according to a statement filed with his plea agreement in federal court.

He was paid $800 by Dauphin, who had told him the detail was to protect a courier worried about getting robbed and for “warning” about “police activity” around the check-cashing store at Northwest 79th Street and Seventh Avenue.

Although Dauphin was not identified by name in James’ plea statement, multiple sources familiar with the investigation said it refers to Dauphin.

James, 29, an eight-year police veteran who resigned in late November, pleaded guilty to two extortion charges Friday. He faces between 1½ and two years in prison at his April 23 sentencing before U.S. District Judge Robert Scola.

James and Dauphin are among at least 10 Miami police officers expected to face federal criminal charges or internal discipline related to the gambling protection scheme and other criminal activities, The Miami Herald has learned.

The FBI is expected to make more arrests in coming weeks.