New Zealand rested its strike bowlers Tim Southee and Trent Boult, and Sri Lanka would have been hoping for a big total after winning the toss on a pitch that captain Angelo Mathews called "a belter."
However Matt Henry swiftly put paid to those plans as he took four wickets for 17 runs in a superb opening spell.
After Adam Milne dismissed Danushka Gunathilaka (8) in the third over, Henry took charge, first by eliciting a false shot from veteran Tillakaratne Dilshan (9) who skied a catch.
He then trapped Lahiru Thirimanne (1) with a full-pitched ball which swung back at the left hander, then removed Mathews — first ball — who played uncertainly outside off and provided a low catch to Tom Latham at second slip.
Just when Sri Lanka was staring at a humiliating capitulation — five wickets down inside ten overs — Siriwardana transformed the Sri Lanka innings and guided the team to a semi-competitive total.
He put on 38 for the sixth wicket with Chamara Kapugedera (8) in a partnership which arrested the decline of the innings, then went on the attack with Kulasekara.
Siriwardana reached his second half century in one-day internationals from 57 balls and went on to his highest ODI score.
Kulasekara was more aggressive, posting his fourth ODI half century from 65 balls and reaching the milestone with his fourth six.
The pair then fell in quick succession as Sri Lanka's innings again went into reverse. Siriwardana fell at 163 and Kulasekara followed an over later at 167.
After their separation Doug Bracewell (3-37) and Mitchell McClenaghan (2-40) were able to wrap up the Sri Lanka tail.
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