A youth product of hometown club Botev Vratsa, he spent two seasons with the first team, before switching to CSKA Sofia in 1975.

In the second round, Yonchev scored a hat-trick for a 4–0 home win over Szombierki Bytom.

[3] On 4 March 1981, he netted CSKA's only goal in a 5–1 loss against Liverpool at Anfield, in their quarter-final first leg tie.

With CSKA Yonchev won five A Group titles and one Bulgarian Cup.

[4] On 3 April 1983, he scored two goals as CSKA beat Spartak Varna 4–0 in the 1983 Bulgarian Cup Final.