Evans' first international try soon after the break put Wales ahead but Maatulimanu Leiataua crossed as Samoa looked determined to bounce back from the 78-0 thrashing by New Zealand.
Evans' second try eight minutes from the end, however, put paid to the hopes of the islanders who effected six changes to go with a position switch for the contest.
It was a gritty display by Robin McBryde's young Wales side who beat Tonga 24-6 at Eden Park last weekend.
With a dozen Wales players on British and Irish Lions duty in New Zealand, the starting 15 had just 151 caps of international experience.
(Reporting by Amlan Chakraborty in New Delhi; Editing by Andrew Heavens)
