Complex sentence: On 25 October 1924, the Helsinki Philharmonic Orchestra premiered the opera at the Finnish National Opera under the baton of Tauno Hannikainen; the enthusiasm of critics and the public quickly elevated the work to the (informal) status of the country's "national opera".
Split into simpler sentences: On 25 October 1924, the Helsinki Philharmonic Orchestra premiered the opera at the Finnish National Opera under the baton of Tauno Hannikainen. The critics and the audience received the performance enthusiastically, immediately elevating the work to the (informal) status of "national opera".