Set a target of 305 for victory in their Pool B opener at Nelson's Saxton Oval, Ireland won with more than four overs to spare after Paul Stirling (92), Ed Joyce (84) and Niall O'Brien (79 not out) made light work of a lacklustre West Indies' attack.
"It's fantastic to win," said Porterfield. "This sets us up nicely for the next few games. Belief has been growing within the squad for a long time and we know what we are capable of."
But Porterfield doesn't want his side to be content with the odd pool win here and there.
"I believe Ireland can qualify for the knockout stages... We just want to keep proving ourselves to the others," he said.
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Ireland, who finished on 307 for six, became the first team at this World Cup to win a match batting second and their victory might have been even more emphatic.
After Porterfield won the toss, Ireland reduced the West Indies to 87 for five, with spinner George Dockrell taking three for 50.