Chasing 233 for victory at Napier's McLean Park, Guptill made 117 off 116 balls, as the Blackcaps reached the target with 33 balls remaining to win by eight wickets.
After missing the final ODI against India and the T20 series with a back injury, Guptill was pleased to see a much-needed return to form, although he admits he was far from his best.
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The 32-year-old is underselling himself though, as he'd scored a combined 62 runs in his last six ODI innings, dating back to his 138 knock in the opening 50-over game against Sri Lanka on January 2.
He now has 15 ODI centuries to his name.
"It still wasn't my fluent best, but to spend some time in the middle and see the team through, I was pretty happy," he said.
"It's always satisfying when you carry your bat, but it was set up by the bowlers in the first innings. They set the tone for the day and made sure Bangladesh didn't get away on us.
"Today wasn't a wicket where you could hit through the line of the ball. It was slow and we had to work hard on it.
"We were able to get through the first 10 overs without losing a wicket and then push on for a big partnership that set up the game."
Guptill combined with Henry Nicholls at the top of the order and the pair had more success than their first outing together - in the Blackcaps' only ODI win over India - where the experiment only lasted a handful of balls.
Nicholls finished with 53 off 80 balls, as the pair combined for an opening partnership of 103 in 22.3 overs.
Unless Colin Munro finishes with a ridiculous score in the final ODI next week, Guptill and Nicholls may open the batting at the upcoming World Cup in the UK.
But Guptill isn't bothered who opens the batting alongside him.
"Who knows?" he said. "It may not work next time, you just don't know.
"I enjoy batting with Henry and I love batting with Colin as well. Whoever I'm opening with, it doesn't bother me too much.
"[Today] It worked well. It set the platform up for the rest of the day for the team to push through and get the win within 45 over.
"The first time didn't last long, but today was good, as we were able to push through a tough period."
Last time the Blackcaps played at McLean Park, the match was stopped for 30 minutes, due to the sunlight shining straight into batsmen's eyes.
Guptill said the issue came up again, but it was more manageable.
"It wasn't easy to bat out there with the sun coming down, but we were able to bat through that and make sure we set the platform.
"We just batted through, to be fair. I have batted at that time before.
"It is not much fun, but if you push on through, you can get through it. It was playable.
"It was spin bowlers bowling at the time, so it wasn't Lockie [Ferguson] bowling at us, which wouldn't have been too much fun. We would have asked for it there."
Join us at 11am Saturday for live updates of the Blackcaps vs Bangladesh ODI at Christchurch.