Ioann Zlatoust and Evstafi forced the German battlecruiser SMS Goeben to disengage during the Battle of Cape Sarych shortly after Russia declared war on the Ottoman Empire in late 1914.

She covered several bombardments of the Bosphorus fortifications in early 1915, including one where she was attacked by the Goeben, but Ioann Zlatoust, together with the other Russian pre-dreadnoughts, managed to drive her off.

Ioann Zlatoust was relegated to secondary roles after the first dreadnought entered service in late 1915 and reduced to reserve in 1918 in Sevastopol.

At full load she carried 1,100 long tons (1,118 t) of coal that provided her a range of 2,100 nautical miles (3,900 km; 2,400 mi) at a speed of 10 knots (19 km/h; 12 mph).

Ioann Zlatoust ran her propulsion trials on 26 July 1910 and reached a maximum speed of 16.2 knots (30.0 km/h; 18.6 mph) and her engines produced a total of 10,623 indicated horsepower (7,922 kW).

They did this successfully on the morning of 17 November and they turned west to hunt for Turkish shipping along the Anatolian coast before setting course for Sevastopol later that afternoon.

They were intercepted by the German battlecruiser Goeben and the light cruiser SMS Breslau the following day in what came to be known as the Battle of Cape Sarych.

Evstafi scored a hit with her first salvo as a 12-inch shell partially penetrated the armour casemate protecting one of Goeben's 15-centimetre (5.9 in) secondary guns.

[10] On 9 January 1915 Breslau and the Ottoman cruiser Hamidiye encountered the Russian fleet while returning from a mission in the eastern part of the Black Sea.

Breslau hit Evstafi's forward turret, temporarily putting it out of action, and the two cruisers escaped using their superior speed.

[12] On 1 August 1915, Ioann Zlatoust and all the other pre-dreadnoughts were transferred to the 2nd Battleship Brigade, after the dreadnought Imperatritsa Mariya entered service.

On 1 October the new dreadnought provided cover while Ioann Zlatoust and Pantelimon bombarded Zonguldak and Evstafi shelled the nearby town of Kozlu.

The British wrecked both ships' engines 22–24 April 1919 when they left the Crimea to prevent the advancing Bolsheviks from using them against the White Russians.