Terziev eventually made his debut for the senior squad, aged 15, in a match against Haskovo on 8 March 2008.

Terziev made his debut in a 4–0 home win against Slavia Sofia on 2 November, coming on as an 82nd-minute substitute for Cosmin Moți.

On 14 November, he made his first start in a 2–1 Bulgarian Cup win over Beroe Stara Zagora, playing full 90 minutes in the centre of defence.

On 12 December, he made his Europa League debut, playing the full 90 minutes in a 2–1 win over Dinamo Zagreb at Maksimir.

Terziev scored his first goal in the Champions League group phase on 26 November 2014, grabbing a 2–2 equalizer against Liverpool in the 88th minute, in an eventual 2–2 draw.