The unorthodox spinner finished with 3-15 off 5.
2 disciplined overs as Sri Lanka dismissed Zimbabwe for a paltry 80 after scoring 210-6.
Mendis, playing his 19th one-day international, broke Indian fast bowler Ajit Agarkar's record of 50 wickets in 23 matches.
Extras were the highest contributor in a dismal Zimbabwean batting performance with 16. Stuart Matsikenyeri (15) was the lone batsman to reach double-figures.
It was Zimbabwe's fourth-lowest total against Sri Lanka in 43 one-day internationals.
Fast bowler Nuwan Kulasekara set up the victory when he grabbed three wickets in his lively opening spell to send Zimbabwe reeling at 27-3 before Mendis and off-spinner Muttiah Muralitharan (2-4) completed the job.
Mendis, who was two wickets short of the record before this game, removed Matsikenyeri and Raymond Price before finishing the match with the dismissal of last-man Tawanda Mupariwa.
Man-of-the-match Angelo Mathews earlier cracked an unbeaten 52 for his maide