''I thought he was going to get the world record as well," New Zealand skipper Brendon McCullum said of Guptill's innings. ''It was a superb innings, you can't describe that. You witness once or twice in your life.
''I know he struck the ball cleanly the other day but jeez he struck it even better today and he did it with such composure.
''Very few players in the world can play like that. He's had a stellar year and he's a huge player for us."
Guptill had the luxury of a first ball let off, clipping the ball down the legside for four, and escaping the clutches of wicketkeeper Dinesh Chandimal off Dushmantha Chameera.
He went on to finish unbeaten on 93 from 30 balls as the Black Caps won by 10 wickets to take a 2-0 lead in the series.
New Zealand skittled the tourists by seven wickets with 29 overs to spare on Boxing Day, but the Sri Lankan batting was worse today - having won the toss, they were dismissed for 117 in 27.4 overs.
Five batsmen got to double figures but none managed more than Nuwan Kulasekara's 19.
Fastest half-centuries in one-day internationals:
Balls - Player - Opponent - Venue - Year
16 - AB de Villiers (South Africa) - West Indies - Johannesburg - 2015
17 - Sanath Jayasuriya (Sri Lanka) - Pakistan - Singapore - 1996
17 - Kusal Perera (Sri Lanka) - Pakistan - Pallekele - 2015
17 - Martin Guptill (New Zealand) - Sri Lanka - Christchurch - 2015
18 - Simon O'Donnell (Australia) - Sri Lanka - Sharjah - 1990
18 - Shahid Afridi (Pakistan) - Sri Lanka - Nairobi - 1996
18 - Shahid Afridi (Pakistan) - Netherlands - Colombo - 2002
18 - Glenn Maxwell (Australia) - India - Bangalore - 2013
18 - Shahid Afridi (Pakistan) - Bangladesh - Mirpur - 2014
18 - Brendon McCullum (New Zealand) - England - Wellington - 2015
Fastest half-centuries by a New Zealander in one-day internationals:
Balls - Player - Opponent - Venue - Year
17 - Martin Guptill - Sri Lanka - Christchurch - 2015
18 - Brendon McCullum - England - Wellington - 2015
19 - Brendon McCullum - Bangladesh - Queenstown - 2007
19 - Ross Taylor - Ireland - Aberdeen - 2008
19 - Brendon McCullum - Sri Lanka - Christchurch - 2015
20 - Brendon McCullum - Canada - St Lucia - 2007
20 - Corey Anderson - West Indies - Queenstown - 2014
21 - Lance Cairns - Australia - Melbourne - 1983
21 - Craig McMillan - United States - London - 2004
21 - Brendon McCullum - Zimbabwe - Bulawayo - 2005
21 - Brendon McCullum - Australia - Auckland - 2015