Chasing a modest 134 for their third straight victory after battling knocks by Nepal's Dipendra Singh Airee (58) and Sompal Kami (26 not out), the Caribbeans eased to victory at Wankhede Stadium with 28 balls to spare.
After pace bowler Holder laid the platform earlier, captain Shai Hope (61 not out) and Shimron Hetmyer (46 not out) took the team home with superb knocks to rule Nepal out of the reckoning for the next stage of the tournament.
'One hurdle crossed'
"I'm very pleased. This is what we set out to do and we got here. That's one step and one hurdle that we've crossed and now on to the next stage," Hope said.
"I'm glad I actually got the opportunity to decide what I wanted to do first. The guys put the ball in the right areas ... It was difficult work for Nepal in the powerplay. Then it was about trying to limit the flow of runs and picking up wickets.
"It's crunch time now, back into the Super Eights."
A little over four months since their confidence-boosting 2-1 T20 series win over a weakened West Indies in Sharjah, Nepal arrived for the clash seeking their first victory in Group C of the World Cup following defeats by England and Italy.
Poor start for Nepal
They made a poor start after being asked to bat by table-toppers West Indies with Kushal Bhurtel bowled by Akeal Hosein on the fifth delivery of the innings and skipper Rohit Paudel trapped lbw by Matthew Forde shortly afterwards.
Holder (4-27) ramped up the pressure by having Aasif Sheikh caught in the deep with a loose ball before Nepal limped to 22-3 in six overs, the lowest powerplay score in this edition of the event silencing a large group of Nepal fans.
Several soft dismissals meant Nepal struggled to recover before Airee cut loose and reached his half-century with a big six, while Kami marked his recall to the side with some late fireworks and took them to 133-8 in 20 overs.
"It was a challenge in the powerplay, their bowlers were using the conditions well," Paudel said. "As a batting unit, we failed again. We need to step up."