Tonga ended on a winning note in Viña del Mar after beating Zimbabwe 19-14 in the playoff for fifth place, have earlier come from behind to defeat Uganda by the same scoreline.
Meanwhile PNG finished in a share of seventh place, having lost 26-19 to Zimbabwe in the previous round.
Both teams were knocked out of title contention in the quarter finals, with PNG outclassed 29-0 by Germany and Tonga overwhelmed 28-7 by host's Chile in the first knockout round.
The Tongans had finished second in Pool A on Saturday after beating Portugal 26-12 and Uruguay 10-0 before a resounding 35-7 defeat by Japan.
The PNG Pukpuks were runners up in Pool B, edging Jamaica 12-10 and Colombia 22-17, either side of a crushing 36-0 defeat by Hong Kong.
The two Pacific Island nations remain on course to reach the final Men's World Series Qualifier in Hong Kong, with the top eight ranked core teams after the two Challenger Series legs in Chile and Uruguay to compete later this year for a permanent spot on the 2021 World Series circuit.
The Olympic hosts Japan will face Germany in the first semi final before Chile take on Hong Kong.