Tim Seifert was the match-winner for the second straight game as New Zealand clinched the T20 series against Sri Lanka with a tense four-wicket victory in Queenstown on Saturday.

Seifert blasted a career-high 88 off 48 balls to fire the Black Caps to 183-6 off 19.5 overs after the tourists had posted 182-6 in the third and final game at John Davies Oval.

The opener-wicketkeeper struck 10 fours and three sixes in an innings that bore many of the hallmarks of his unbeaten 79 when New Zealand levelled the series at Dunedin on Wednesday.

Captain Tom Latham provided the only meaningful support with 31 off 23 and New Zealand's middle order nearly conspired to lose the game after Seifert departed with four overs remaining.

Needing to score at little more than a run-a-ball at that stage, the Black Caps stuttered.

Needing 10 runs to win off the final over bowled by Lahiru Kumara (3-38), Mark Chapman struck a six off the first ball before he was the first of three New Zealand wickets to fall.

With two still needed off the last two deliveries, Rachin Ravindra held his nerve to find a gap in the outfield and ran two to secure the 2-1 series win.

It completes a disappointing tour for Sri Lanka, who lost the Test and ODI series by the same 2-0 scoreline but were more competitive in the shortest format.

They gave themselves a shot at victory after Kusal Mendis struck a rapid 73 off 48 balls, taking full advantage after being dropped by Daryl Mitchell at slip when on 10.

The opener-wicketkeeper went on to hit six fours and five sixes in his 12th half-century, falling just short of his career-high score of 79.

Having been asked to bat, Mendis was the dominant figure in an opening stand of 76 with Pathum Nissanka (25 off 25), before putting on a further 46 with Kusal Perera (33 off 21).

Wickets fell rapidly over the closing overs, preventing the tourists from going close to 200.

Ben Lister took 2-37 while fellow-seamer Adam Milne and leg-spinner Ish Sodhi were the most economical of New Zealand's bowlers, recording identical figures of 1-30 off four overs.