The Rugby League World Cup has been littered with blowouts to start, but Tonga has won a thriller 24-18 against Papua New Guinea thanks to a last-gasp try.

The Tongan outfit stacked with NRL talent had to wait until the 78th minute for South Sydney's Keaon Koloamatangi, who played a lengthy stint at hooker, to touch down.

The Kumuls only had two established NRL players — fullback Alex Johnston (Souths) and centre Justin Olam (Melbourne) — in their starting team, but comfortably accounted for the Tongans for the majority of the match.

That was reflected in the fact that with 10 minutes to go the scores were tied 18-18 in front of 10,409 fans at St Helens's Totally Wicked Stadium.

PNG, which was a $12 outsider, had begun ominously when skipper Rhyse Martin scored after six minutes.

Winger Dan Russell, who was a late inclusion for Xavier Coates, was unlucky to not have followed him over the line twice.

Tonga was under the pump and a Will Penisini try against the run of play sent the small legion of fans decked out in red into a frenzy.

Moeaki Fotuaika and 18-year-old Dolphins-bound half Isaiya Katoa both crossed off the back of long-range tries to put Tonga back in control with an 18-6 lead at half-time.

But that was immediately shortened when Kumuls playmaker Lachlan Lam scored in the first minute of the second half.

After receiving the kick-off, PNG's powerful opening set was punctuated by a superb line break from dummy half by man-of-the-match Edwin Ipape, who popped an offload to a supporting Lam to touch down.

And despite having a try for winger Rodrick Tai chalked off, the Kumuls kept pushing and they got their reward when Toulatau Koula knocked on at a play-the-ball on the Tonga line.