[2] On Sept. 17, 1939, Yeryomenko led his 6th Cavalry Corps into eastern Poland as part of the operations agreed to between Germany and the Soviet Union under the Molotov–Ribbentrop Pact.

Yeryomenko (whose Corps contained light tank and other motorized elements) was forced to request an emergency airlift of fuel so as to continue his advance.

The Nazi Blitzkrieg approach to warfare quickly dominated the Western Front, but Yeryomenko motivated the remaining troops, and halted the German offensive just outside Smolensk.

Stavka, particularly Stalin and Shaposhnikov, seemed convinced that Yeryomenko could block or distract Guderian's drive and save Kiev from encirclement.

Most of Yeryomenko's weakened forces (3rd, 13th and 50th Armies) were partially encircled by Oct. 8[6] although small units managed to escape for days or weeks following.

During the Soviet Winter Counteroffensive, Yeryomenko's army was part of the highly successful Toropets–Kholm Offensive, which liberated Toropets and much of the surrounding region, helping to create the Rzhev Salient, which became a major battlefield over the next 15 months.

Yeryomenko and Commissar Nikita Khrushchev planned the defense of Stalingrad, rallying and re-organizing men and equipment falling back to the city from the Don River and the steppes to the west.

During Operation Uranus, November 1942, Yeryomenko's forces helped to surround the German 6th Army from the south, linking up with the northern penetration at Kalach-na-Donu.

Yeryomenko successfully repelled the attack, largely with the forces of the 2nd Guards Army along their fall-back positions on the Myshkova River.

In December, Yeryomenko was once again sent south, this time to take command of the Separate Coastal Army, which was put together to retake Crimea, which was accomplished with assistance from Fyodor Tolbukhin's 4th Ukrainian Front.