Following Denikin's defeat, Yakovlev crossed the Bolshevik lines and with his men joined the Red Army as the commander of the 3rd Don Cossack Cavalry Brigade.
Attached to the Semyon Budyonny's 1st Cavalry Army, the brigade was dispatched to the front of the Polish-Soviet War during the Polish offensive on Kiev.
After the Battle of Wołodarka on 31 May 1920, he again switched sides with his men and joined the Polish Army, where his grade was reaffirmed as that of a Colonel.
The troops of Yakovlev were particularly notorious for their cruel and bloody marauding of villages and towns in Ukraine and, later, Belarus, and anti-Jewish pogroms in the early 1920s.
[1] After the cease-fire agreement in late 1920, Yakovlev signed an alliance with the exiled government of the Ukrainian People's Republic and decided to continue the struggle against the Reds.