Sri Lanka have suffered another major injury setback with right-arm pacer Lahiru Kumara being ruled out of their ongoing Australia tour.
Mendis left the field immediately and spent the rest of the day icing the injury to his right ring finger.
Tim Southee top scored with 68 and finished the day with three wickets after the BlackCaps were bowled out for 178.
Sri Lanka enter the series against New Zealand on the back on a 3-0 series whitewash against England at home.
Sri Lanka need 63 to win to level the series as well as become the first Asian side to win a Test at Kensington Oval.
West Indies were bowled out for 204 despite a gritty lower middle-order resistance. However, they struck back to reduce Sri Lanka to 99 for 5.
Only Michael Holding and Courtney Walsh have better figures.
India suffered a setback after being drubbed by five wickets in the opening tie against Sri Lanka in Pune.
Either Indian loses or win, record books has to be updated.
Shikhar Dhawan was dismissed for mere nine by fast-bowler Kasun Rajitha after being caught by Danushka Gunathilaka against Sri Lanka.