Captain John Reed told reporters the fourth crew member is stuck behind glass in a control room, but teams would "find a way to get him".
Rescuers drilled a hole near the ship's stern to get to the trapped crewmen.
Car carrier the Golden Ray overturned early on Sunday morning after leaving the port of Brunswick.
Authorities only managed to save 20 of the crew before fire forced them back. On Monday, they managed to make contact with the remaining four and drill into the hull.
Those remaining on board are all South Korean nationals, the country's foreign ministry said.
Capt Reed said crews heard the trapped men tapping the hull, which helped them to find where they were in the ship. "I think that really motivated the team here," he added.
Rescue teams drilled a hole into the hull of the ship to get food and water to three of the men, who were trapped near the propeller shaft.
These three have since been rescued, and have been taken for emergency medical treatment. Two were able to walk, Capt Reed said, but he did not comment on the third's condition.
"They were subject to some pretty tough conditions over the last day and a half," he told a press briefing. "They looked super happy to be outside that space."
The fourth man however is trapped in a separate part of the ship from his rescued shipmates. Crews have not managed to get him food and fresh water.
Footage from the scene showed a US coastguard helicopter landing on the heavily listing Golden Ray, and rescue teams assessing the vessel's hull.