Ramos, 33, has been an ever-present since making his international debut in 2005 and featuring on Sunday leaves him on the brink of history.
The centre-back was a key player in Spain's greatest international triumphs, helping them to European Championship success in 2008 and 2012, as well as their first World Cup title in 2010.
Casillas had been out in front by himself ever since retiring from international football in 2016, but Ramos is now just a single appearance from setting a new outright record.
🔝¡ENHORABUENA, CAPITÁN!🔝— Selección Española de Fútbol (@SeFutbol) September 8, 2019
Estamos viviendo un momento histórico. Con este partido, @SergioRamos iguala a @IkerCasillas como el futbolista que más veces ha vestido nuestra camiseta (167).
The Real Madrid captain will likely remain at the top of the pile for a significant period of time, with Sergio Busquets the closest active player with 114 caps.
Ramos was the one constant from the backline that lined up in the 2-1 win over Romania last time out, as David de Gea, Dani Carvajal, Mario Hermoso and Jose Gaya came into the team.
Coach Robert Moreno – still deputising for the absent Luis Enrique whose daughter recently died – also rang the changes in midfield and attack.
Rodrigo Moreno retained his place, but otherwise Spain were completely refreshed, with Suso, Mikel Oyarzabal, Thiago Alcantara, Rodri and Dani Parejo starting.
Spain have won all five of their Euro 2020 qualifiers and were expected to continue that run in Gijon.