Berg was Sweden's main striker during the 2018 FIFA World Cup qualification after the retirement of Zlatan Ibrahimović. He scored his first goal in the qualifiers on 6 September 2016, the opener of the 1–1 home draw against Netherlands. On 7 October 2017, Berg scored four goals as Sweden ran riot in front of a record crowd of 50,022 at the Friends Arena, hammering Luxembourg 8–0, in their biggest win in 79 years, to make a great step to the 2018 FIFA World Cup finals. It was also his 50th international appearance. Sweden eventually finished Group A on second place with 19 points with Berg as top goalscorer with 8 goals. At second round, Sweden faced Italy and eliminated them 1–0, returning at the World Cup for the first time since 2006; Berg was distinguished for his defensive work rate in the second leg.