In the second round, the Russian delivered an accurate blow to the solar plexus, and then finished off the opponent.
Thus, Volkov won by technical knockout.
For the Russian fighter, this victory was the 32nd with eight defeats in MMA.
Harris suffered his ninth career defeat in 13 battles won.
The main event of UFC 254 will be the fight for the title of the champion of the Ultimate Fighting Championship in lightweight between Khabib Nurmagomedov and Justin Gaethje.
RT conducts an online text broadcast of the battle.
Previously, Philip Howes knocked out Jacob Malkoon in 19 seconds at UFC 254.