NEW YORK (Reuters) - Duke Energy Corp (>> Duke Energy Corporation), which closed its $18 billion buyout of Progress Energy this week, said on Tuesday that Progress Chief Executive Bill Johnson had resigned and would not be taking the top job at the combined company as had been planned.

Duke CEO Jim Rogers, 64, will become CEO of the combined entity, while remaining chairman, the company said. Rogers said in an interview that he had been officially notified of his new role after board deliberations on Monday afternoon.

"I have done two combinations before. The first focus must be on bringing the companies together and empowering the leaders to move forward, capture the synergies and make sure at the same time we continue to provide affordable and reliable service," Rogers said.

Duke said Johnson's resignation was by "mutual agreement". Johnson, 58, could not be immediately reached for comment.

The deal, first announced in January 2011, closed on Monday after receiving clearance in the Carolinas and by federal regulators. It creates the largest U.S. power company with 7.1 million electricity customers in North Carolina, South Carolina, Florida, Indiana, Kentucky and Ohio, and 57,000 megawatts of generating capacity.

Rogers said he was contacting the company's key regulators to discuss the management changes.

Ann Maynard Gray, Duke's lead director, said Johnson had been "instrumental in helping us close the merger with Progress Energy, and we wish him well in his future endeavors".

Gray, on a conference call, declined to comment further about the executive change.

At least one analyst expressed concern Duke could lose senior Progress executives, many of whom are loyal to Johnson.

Rogers said on the conference call that he had contacted Progress executives on Monday night "and talked through where we're going in the future and how we have to pull together".

"My expectation is that all will lead and make this a great success," Rogers said.

(Editing by Gerald E. McCormick, Maureen Bavdek and Dale Hudson)

By Michael Erman and Ernest Scheyder

Stocks treated in this article : Duke Energy Corporation, Progress Energy, Inc.