With their scoring outburst, Belgium finished atop Group G and will face a third-place finisher on Wednesday in Seattle. Friday's match was played simultaneously to the other group finale in Seattle between Egypt and Iran, which ended in a 1-1 draw.
The Belgians went into the match a surprising third in their group after opening the World Cup with a 1-1 draw against Egypt and a scoreless draw against Iran.
Kevin De Bruyne, Romelu Lukaku and Alexis Saelemaekers also scored for the Belgians, who were eliminated in the group stage in Qatar four years ago after finishing third at the 2018 World Cup in Russia.
"I think we had the chances as well in the first two games, and we didn't take them. So it's important that we took them today," Trossard said.
Elijah Just scored the goal for New Zealand, who needed to win outright to have a chance at advancing. The plucky All Whites head home without a first-ever World Cup win despite having led both Iran (drew 2-2) and Egypt (lost 3-1) in their first two matches.
Should Belgium win their knockout round opener, twey will face the winner of the match between the United States and Bosnia-Herzegovina in the round of 16.
Trossard came oh-so-close to scoring early in the match, but goal-line technology determined that the ball did not cross the line.
In a scramble in front of the net, Trossard popped the ball up into the cross bar and it fell into the goal to put Belgium in front in the 28th minute.
It was Belgium's first goal at the World Cup since Michy Batshuayi's goal against Canada in the group opener in Qatar in 2022. Belgium's goal in their 1-1 draw against Egypt in the opener of this tournament was an own goal.
Trossard scored his second early in the second half, striking a rebound off a New Zealand player past goalkeeper Max Crocombe.
De Bruyne added a stunning strike from outside the box in the 66th minute to all but put the game away for Belgium.
There was a flurry of late goals. Just's goal avoided the shutout for New Zealand in the 84th minute, but two minutes later substitute Romelu Lukaku scored on a header for Belgium then Saelemaekers scored in stoppage time.
"It's been a long journey, and proud of the boys," said Just. "Everyone worked their hardest, It just wasn't there."
Winger Jérémy Doku started for Belgium after missing Sunday's scoreless draw with Iran with an illness. He then flew to London for the birth of his son. He had only trained with the team once in seven days.
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