It only took a minute into the second round before Thomas found himself defeated, when the Swede received a hard left hook, writes Sportbladet.
Tonight's match was Wallin's first since changing coaches to Ronnie Shields, who previously trained Mike Tyson, among others.
34-year-old Wallin from Sundsvall has won 28 fights during his professional career, 16 of which by knockout, and only lost three. His last loss came against Briton Derek Chisora in Manchester in February.
