Hulyanytsky's most noted exploit during the Muscovite invasion was the defence of Konotop. Hulyanytsky and his men (estimated to be around 4,000) held the fortress for 70 days against the 28,000 strong army of Prince Trubetskoy. Hylyanytsky's stubborn defence of Konotop was instrumental in defeating the invaders when Ivan Vyhovsky in alliance with Crimean Tatars and Poles routed the Muscovite army at Konotop on June 29, 1659.