Clue: Long flip working, Arsenal's first scored by Gunners great (sadly lost) (5,8)
Answer: DIEGO MARADONA
Explanation: Definition: great (sadly lost)
**DIE** ("long") + **GO MAD** ("flip") + **ON** ("working") + **A**(rsenal) ['s first] *scored by* **RA** (Royal Artillery, so "Gunners")