Three O'Clock Blues was B.B. King's first big hit in 1952.
West Coast(via Tulsa) bluesman Lowell Fulson recorded it first in 1946 and it was a hit when it was released in 1948. I think you will recognize how B.B. made it a classic.(Fulson also was the first to record "Tramp" which Otis Redding made a hit.)
Naturally, the tune became a staple of B.B. King's live shows over the years.And here's the up and coming Gary Clark Jr. playing it very much in a B. B. vein.