After the union of the two Pirin clubs from Blagoevgrad in December 2008, Delev joined the part of the team, which plays in the top division. On 4 March 2009, he scored a goal in a match against CSKA Sofia for the Bulgarian Cup and Pirin eliminated their opponent. In the semi-final of that tournament against Levski, Delev had a tragic accident. After spasm of the lungs he remained to lie on the grass, and later was sent to emergency hospital. It was later found out that he had played with a flu. Delev made his A PFG debut on 8 March, in a match against Cherno More. On 5 April, he scored twice against Belasitsa Petrich. Those were his first goals in A PFG. On 11 June, Delev was named the Best Young Footballer of the 2008–09 season in Bulgaria. Just 19, Delev's goals helped Pirin to reach the Bulgarian Cup final.
CSKA Sofia
On 27 June 2009, Delev joined CSKA on one-year loan for 2009–10 and later signed a three-year contract. He scored his first goal for CSKA in the second-leg of the UEFA Europa League play-off of against Dynamo Moscow on 27 August 2009, bringing the score to 1–1 with a header. Delev netted the third goal in the victory over The New Saints in the UEFA Europa League play-off. On 16 December 2010, he found the net in a 1–3 away loss to F.C. Porto in the Europa League group stage. He also scored two goals in the Bulgarian Cup semi-final against Litex Lovech on 20 April2011, as well as the winning goal against Slavia Sofia in the final on 25 May 2011. During the 2010–11 season he managed 13 goals in the league.
Mersin Idmanyurdu
On 12 January 2012, Delev signed a 3,5-year contract with Turkish side Mersin İdmanyurdu. Delev's debut came on 15 January, in a 0–2 home loss against Antalyaspor in a Süper Lig match, during which he appeared as a second-half substitute. On 24 January, Delev netted his first goal for the team, opening the scoring in a 1–2 home loss against Kayserispor. In June 2012, he dissolved his contract due to financial reasons.
CSKA Sofia
After seven months without a club, Delev returned to CSKA Sofia on 31 January 2013.
On 20 June 2016, Delev signed for Polish side Pogoń Szczecin on a three-year contract. He made his Ekstraklasa debut on 16 July, replacing Mateusz Lewandowski in the 66th minute of Pogoń's 2–1 loss against Wisła Kraków. He scored his first goal in a 4–0 away win against Kalisz in a game of Polish Cup on 10 August. His first league goals for Pogon came on 29 October when he scored twice in a 2–1 home win over Ruch Chorzów. He scored a brace in a 2-4 away win against Nieciecza, on 17 March 2018.
