''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."
New Zealand reached the target off only 8.2 overs, Latham finishing on 17 off 20 balls, and hitting the winning runs.
Guptill's innings included nine fours and eight sixes and the ground simply wasn't big enough for him.
He was responsible for 27 coming off speedster Dushmantha Chameera's second over, and 26 from the first over in ODI cricket by legspinner Jeff Vandersay.
Sri Lanka, having won the toss, produced an even poorer batting display than they had on Boxing Day, when beaten by seven wickets with 29 overs to spare.
They were dismissed for a paltry 117 in just 27.4 overs.
Five batsmen got to double figures but none managed more than Nuwan Kulasekara's 19.
Sri Lanka were in trouble early when key batsman Tillakaratne Dilshan was out in the fourth over, lobbing a catch to first slip off seamer Matt Henry when he charged initially then seemed to change his mind and fended the ball off his glove.
Lahiru Thirimanne and Danushka Gunathilaka departed within five balls shortly after, the former steering an upper cut straight to third man, the latter out to a fine diving catch at cover by Mitchell Santner.
Sri Lanka's wheels were wobbling at 31 for three and they desperately needed something of substance from their two best batsmen, captain Angelo Mathews and Dinesh Chandimal.
No such luck. Chandimal went lbw to Doug Bracewell to start a slide of five wickets in 37 balls.
Mathews played some pleasant strokes before touching a leg side catch to wicketkeeper Luke Ronchi off left armer Mitch McClenaghan.
Milinda Siriwardana pushed McClenaghan to the point where Henry Nicholls took a low catch before Chamara Kapugedera was run out in a shocking mixup.
Kulasekera turned his back on his partner to ensure he got back to his crease first, leaving Kapugedera stranded.
The rest folded but at least Sri Lanka passed their lowest score against New Zealand, 112 at Christchurch eight years ago.
Henry finished off the innings, and for the second time in three days had the best figures, four for 33 off 9.4 overs.
McClenaghan took three for 32 with one apiece to Bracewell and legspinner Ish Sodhi, one of whose overs included two DRS referral appeals. Sri Lanka's was successful; as was New Zealand's a couple of balls later.
Game three is in Nelson on Thursday.
SCOREBOARD
WAGONWHEEL
MANHATTAN