Gunathilaka who reached his half-century off 59 balls struck 12 fours and one six in his innings and featured in a century (116) opening partnership with Lahiru Thirmanne who made a solid 45 off 83 balls (6 fours) as Sri Lanka ended the day at 160 for two wickets.
Earlier New Zealand XI recovered from their overnight score of 67-4 to take a 60-run first innings lead by scoring 270-8 before declaring their innings.
Twenty-year-old Sandeep Patel from Auckland hit an impressive 69 off 106 balls (7 fours).
The Lankan bowlers failed to finish off the tail after reducing the home side to 191-7 with 19-year-old Katene Clarke (46), captain Peter Younghusband (31 n.o.) and 18-year-old Max Chu (33 n.o.) putting up stern resistance.Spinners Dilruwan Perera and Lakshan Sandakan took two wickets apiece.This is Sri Lanka’s only warm-up match ahead of the two-Test series against New Zealand which starts at Wellington on December 15.