Ireland, having beaten West Indies and Zimbabwe so far, are in the hunt for a last-eight spot and will face India in Hamilton on Tuesday.
"No, I don't think their guard will ever be down. They're a squad of 15, so whatever they decide to do, they decide to do," Porterfield told reporters after the five-run triumph over Zimbabwe here.
"We've just got to keep all the momentum going and keep on improving at the little things we want to and keep taking things forward," he added.
India are unbeaten in the event so far, having already edged past fancied rivals such as Pakistan, South Africa and the West Indies en route to qualifying for the quarterfinals.
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Ireland, on the other hand, are currently fourth on the points table and have earned the reputation of giant-killers after beating at least one Test-playing nation in each of the three previous World Cups.
"We just tried to break it down really and take each game as it comes, and whatever we need coming down to the last game, we need, but as I said, we just take this India game now and that's all we can look forward to.
"We've managed to deal with the West Indies game and the UAE game and not look past them, and there's so many things that can happen in all our games and so many things have happened," he explained.