Together with BoIS' other forward, Danijel Milovanović, both of them became a feared top-duo that led their recently promoted club to the top position of Allsvenskan at the break for the World Cup in Japan and South Korea. After the eight first matches, Landskrona BoIS had won five matches, drawn three times and never lost. When forward colleague Milovanović got seriously injured against rivals Malmö FF (an injury from which Milovanović never recovered), this surprising success ended for Nannskog's club, but Nannskog himself continued to score. Nannskog left Landskrona BoIS in summer of 2003 to join the Chinese club Sichuan Guancheng on a two-year deal. He went on to stay for a year-and a half, but terminated his contract in order to play for his old coach Janne Jönsson at Stabæk in the 2005 season. His first season at Stabæk was very successful, with his club being promoted in style. "The Body" Nannskog was also named top scorer with 27 goals in 29 games. Nannskogs debut in the Norwegian top division was successful. They finished fifth, just outside an UEFA Cup spot. Nannskog was crowned top scorer with his 19 goals, one goal ahead of team-mate Veigar Páll Gunnarsson. Nannskog and Stabæk continued their progress, and for a second time in a row, he managed to score 19 goals, but this time finishing behind Brann's Torstein Helstad, who scored 22. However, Stabæk did better in the league, finishing second behind Brann. They were in front half way, but did not have the edge in the second part of the season. Stabæk have played well in the first part of the 2008 season with Nannskog an integral part, like when he scored two goals in the away match against Ham-Kam (2–0 victory) in round 5 . The Norwegian media felt it was time the Swedish national team took a look at him again with a possible inclusion in the Euro 2008 squad, following his winning goal against Rosenborg on 4 May. However, he did not make the squad. On 14 September Nannskog scored four goals in a 6–0 victory over Strømsgodset, taking him to the top of the goal scoring chart with 13 goals – helping Stabæk with a six-point advantage with six rounds to go.