Argentina bounced back from their opening-round defeat to France with a 28-12 victory over Tonga in Osaka.
Two early tries from hooker Julian Montoya, both converted by Benjamin Urdapilleta, put the Pumas 14-0 in front after 18 minutes of the Pool C clash.
Argentina were gifted a third try shortly afterwards as Tonga failed to pick up a loose ball and centre Santiago Carreras raced clear for his first try for his country. Urdapilleta had a simple conversion underneath the posts.
The TMO ruled Urdapilleta came up short of the line after 24 minutes, but Montoya ploughed over to complete his hat-trick moments later, earning Argentina a bonus point as they made it 28-0.
Tonga got on the board before the break as Leicester Tigers winger Telusa Veainu broke through following some patient build-up play and Sonatane Takulua converted.
David Halaifonua was denied a second try by the TMO before the break as Tonga went in 28-7 down.
The second half was a much tighter affair, with superb defence from Takulua preventing Tomas Cubelli from scrambling over a fifth try.
Tonga scored the only try of the second half, with Veainu going over again after great strength from Cooper Vuna. Takulua's conversion made it 28-12, and that was how it stayed.
Montoya was unaware that his hat-trick of tries had made him the top scorer at the World Cup, but spoke of his pride at representing his country.
"I didn't know that," a surprised Montoya told Rugby World Cup 2019's Twitter feed after learning he was the tournament's leading try scorer.
"It's something nice but the more important thing is playing for my country, my family, my friends, my club, my girlfriend and all the people I care about. I want to make them proud of me.
"It was a really tough match and I'm really happy with how the team played, especially in the first half.
"The second half we were good but we need to make better choices when we are in their half of the field."
Tonga captain Siale Piutau rued a slow start to the game.
He said: "We wanted to start well, which we didn't, and we gifted Argentina some easy tries in the first half and that made it difficult to climb back.
"We improved our physicality from last week and wanted to bring that into this game, but we brought it just a bit too late."