Even if they lose, a first victory for their associate colleagues United Arab Emirates over West Indies would send the Irish through.
But with the International Cricket Council controversially cutting the number of teams from 14 to 10 for the 2019 tournament, defeat for both UAE and Ireland on Sunday would likely mean a long wait for another World Cup chance.
Ireland have three wins from five games here, but UAE, Afghanistan and Scotland have lost 15 of 16 matches to offer some justification to the ICC's decision.
Porterfield, though, felt those losses did not paint the whole picture.
"I think all teams in the competition have shown enough to justify a change in 2019," the 30-year-old, who was part of the Irish team that beat Pakistan at the 2007 World Cup, told reporters.
"Afghanistan could have gone across the line against Sri Lanka ... which would have been great for them to get that win.
"But I don't think it should matter. We've shown enough regardless come tomorrow of where we're at and where the next qualifiers are at."
Ireland and Afghanistan have the best shot of the four to make the 2019 World Cup after the ICC added the duo to the rankings-based qualification system along with the 10 full test playing nations.
Hosts England and the top seven sides as of September 2017 will qualify for the next World Cup, with another two coming from another qualifier for the bottom four and six other associate sides.
But the chances of success for Ireland and Afghanistan will depend on the amount of fixtures they will be able to play to help their ranking.
And that is a concern for Porterfield.
"We've played nine against the top 10 in the last four years, and I'm sure that's a lot more maybe by Afghanistan. UAE and Scotland wouldn't have played that many," the Northern Irishman said.
"So accumulative among the four countries, we've probably played as many in four years as a lot of teams play in one year, if not less.
"So in terms of coming into this competition, I think the qualifiers have prepared themselves very well considering the preparation over the four years. I think to be able to do that with that little preparation is great."
(Writing by Patrick Johnston in Singapore; Editing by Peter Rutherford)
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