There was a brief period when Kostas Peristeridis displaced him from top spot again after young Giannakapoulos oversaw a run of 3 straight defeats.
Arguably his best performance came in the early part of his career when he kept a clean sheet against Greek giants, Panathanaikos.
He repeated this feat the following season as Panionios beat Panathanaikos 3–0 with Giannakopoulos as a main goalie.
As he is not among the first priorities of Panathinaikos coach Andrea Stramaccioni he signed a long-term year loan with Cypriot club Aris Limassol FC.
[7] On 4 July 2018, following Kerkyra's relegation to Football League, he joined Panetolikos on a two-year deal.