Iran Press/Europe: Roberto Martinez's world-number-one-ranked Belgians only had to avoid defeat to qualify from Group A2 but secured a finals spot in style.
Lukaku has now scored 17 goals in his last 14 international games after his second-half double.
Italy needed a win in Sarajevo to be sure of progress from Group A1, but had little trouble in beating Bosnia 2-0.
Andrea Belotti scored the opening goal, with Sassuolo's Domenico Berardi netting for the second straight game.
Belgium and Italy join world champions France and Spain in qualifying for next October's finals.
The 2020–21 UEFA Nations League is the second season of the UEFA Nations League, an international association football competition involving the men's national teams of the 55 member associations of UEFA.
Portugal were the defending champions, having won the inaugural 2019 finals.
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