Ronald Koeman arrived at Benfica on 8 June 2005 on a two-year deal, four months after being dismissed by Ajax. He inherited the reigning Portuguese champions from Giovanni Trapattoni and started with silverware, beating Vitória de Setúbal 1-0 on 13 August 2005 to win the Supertaça Cândido de Oliveira, Benfica's first in fifteen years.

Europe was the highlight of his single season. Drawn with Manchester United, Villarreal and Lille, Benfica finished second and knocked United out at the group stage, then eliminated holders Liverpool 3-0 on aggregate to reach the Champions League quarter-finals for the first time in eleven years, going out to Barcelona.

Domestically it unravelled. Benfica finished third, twelve points behind champions Porto and five behind Sporting, and lost a Taça de Portugal quarter-final to Vitória de Guimarães.

Koeman conceded he had not done everything he could in the league and resigned in May 2006 to take charge of PSV Eindhoven. His reign lasted one season, but the run past United and Liverpool is still fondly remembered at the Luz.