These events launched his North American career, which flourished until it came to a sudden halt in 1953; while walking through New York's Central Park, Lewenthal was attacked by a gang of hoodlums and suffered broken bones in his hands and arms.
After a slow physical and psychological recovery, Lewenthal moved abroad and withdrew from the concert stage except for occasional touring and recording in Europe and South America.
Encouraged by the reception, Lewenthal played a recital including Alkan's music in Town Hall, New York, in September 1964 - his first public appearance there in 12 years.
This led to an RCA recording of Alkan's music which was met with critical raves, and then a three-concert Liszt Cycle in New York and London, among many other performances.
Lewenthal came to be considered the leader of the "Romantic Revival", reintroducing solo and chamber works by many important but neglected 19th-century composers such as Moscheles, Goetz, Herz, Hummel, Henselt, Scharwenka, Rubinstein, Reubke, Field, Dussek and others, as well as reviving overlooked works by famous composers.
Lewenthal also prepared for the same publisher an anthology called Piano Music for One Hand and another collection of Encores of Famous Pianists, both containing extensive notes and commentary.