In December 1939 Borisov served in the 1st eskadrilya of 5 IAP-KBF, which during this time was equipped with Polikarpov I-153s.

On 23 December he claimed a Finnish VL. Kotka near Paldiski. This was 5 IAP-KBF’s first victory during the war.
At 12.45 (Finnish time) a Blackburn Ripon IIF (RI-155) of LeLv 36 had taken off for a reconnaissance sortie to Paldiski. The aircraft was flown by 24-year-old kersantti Kaj Uolevi Söderholm and with the 24-year-old observer vänrikki Esko Antero Huhanantti. The aircraft was last observed at 13.10 from Mäkiluoto fort (40 km SW Helsinki). At 13.45 an explosion was seen in the air in direction 210 degrees. A Soviet radio message about a shot-down Finnish reconnaissance aircraft at Pakri was intercepted 14.05, one crewmember (Huhanantti) tried to escape by parachute from the burning aircraft but both crewmembers were unfortunately killed. It is very possible that this was the aircraft claimed by Borisov.
It has been written that vänrikki Esko Huhanantti was shot and killed by the enemy fighters while hanging under his parachute. His brother luutnantti Tatu Huhanantti, LeLv 24, took this rather badly and at least on one occasion avenged his brother by killing a Russian airman who had jumped from a falling aircraft. Tatu Huhanantti was killed in action on 29 February 1940 after claiming six victories.

During the Winter War Borisov flew ten sorties but on 25 December 1939 he was shot down and killed while attacking a Finnish AA battery on the Hanko peninsula.

On 7 February 1940 he was posthumously awarded the Gold Star of the Hero of the Soviet Union.

At the time of his death Borisov was credited with 1 biplane victory.

Claims:

Kill no.	Date	Number	Type	Result	Plane type	Serial no.	Locality	Unit
	1939
1	23/12/39	1	VL. Kotka (a)	Destroyed	I-153		Paldiski area	5 IAP-KBF

Biplane victories: 1 destroyed.
TOTAL: 1 destroyed.
(a) Possibly Blackburn Ripon IIF RI-155, which was lost in the area during the day. This aircraft was flown by kersantti K. Söderholm and with the observer vänrikki E. Huhananti.

Sources:
Kohtalokkaat lennot 1939-1944 - J.Hyvönen kindly provided by Carl-Fredrik Geust
Protiv Finlandii - S. V. Tirkeltaub and V. N. Stepakov, ISBN 5-93414-015-9 kindly provided by Tomáš Polák
Suomen sodissa 1939-1945 menehtyneiden tiedosto
Additional information kindly provided by Carl-Fredrik Geust and Jari Lappalainen