It wasnt the Ottoman regular army it was small vanguard units checking where until they can push with no resistance from enemy. The Bosnian victory could be decisive but the battle herself wasnt decisive for this reason. It's like when Serbian forces defeated another small Ottoman vanguard troops in Ploshnik in 1387.
https://en.wikipedia.org/wiki/Battle_of_Plo%C4%8Dnik
We lost here because Serbian forces ambushed Ottomans in mountain and highland regions in Niş Sofya region.
The sultan didnt participate himself to both as he was fighting in East for Seljuk bakiya city of Konya against Karamanids who were also Muslim Turks. Karamanids were more serious threat for Ottomans then any Balkan forces.
However after these small defeats the Serbian administration felt audacious and there was plan to organize a huge crusade together with Hungarians and Wallachians. This is when Murad 1 decided to solve the Serbian-Bosnian question.
And Murad chose Kosovo which wasnt mountains and the year 1389 so right after these two insignificant battle to deliver the decisive battle. Murad was present in Kosovo, the Serbian king Hebrelyanovic was present in Kosovo and also the Bosniak commander winning in OP referred battle Vladko Vukoviē was also present in Kosovo. The Ottomans won the decisive victory and it was Bayezid's Ottoman right flank storm against Bosnian forces of Vukovic (Crusaders left) which broke the Serbian lines, Serbian center flanked and Hebrelyanovic killed in combat also Pal Kastrioti from that Albanian noble family was among the dead. All this I say to say this was more like skirmish than decisive battle.
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