Five goals in the first round, then three in the second, and now six in the third round... Građanski stepped into the season in furious style, ultimately becoming double champions. The Zagreb side finished first in the Croatian-Slovenian League, which also served as the qualifying group for the Kingdom of Yugoslavia's national championship. Građanski continued to soar at the top of the table throughout the competition and claimed the national title.

In the 3rd round clash of the Croatian-Slovenian League, the Zagreb team was hosted by Bačka in Subotica, a sports club supported by the Croatian community. Bačka is also the oldest club in the territory of former Yugoslavia, founded back in 1901. The full name at that time was Croatian Sports Society Bačka. One of the club's members, Marko Čović, was also secretary of the Croatian Football Association and a member of the Croatian Sports Union board as the main sporting body during the Croatian Banovina period.

The media highlighted that Građanski's visit to Subotica was a major sporting and national event, especially since members of the Croatian Sports Union and HNS also attended the match.

It was on this very occasion, on the same day, September 10, 1939, that the Bačka Football Sub-Association was established as an organization of Croatian clubs from that region, operating under the auspices of the HNS.

Građanski convincingly won 6-0 on the pitch, with the match watched by 3,000 spectators, which according to media reports was a record attendance for any sporting event in Subotica.

Miroslav Mirko Kokotović scored twice, while August Lešnik, Franjo Mara Wölfl, Dragutin Žalant and Milan Antolković each found the net once. After three rounds, Građanski sat at the top with maximum points and an impressive goal difference of 14-0. In the previous two rounds, their opponents were Ljubljana, whom they defeated 5-0, and city neighbors Concordia, whom they beat 3-0. Exactly half of those 14 goals, seven of them, were scored by Lešnik.