Jorge Jesus lamented the impeccable display of former Benfica goalkeeper Roberto in their 1-0 defeat to Olympiacos on Tuesday.
Benfica started the match well and created two chances within the first 10 minutes, but Oscar Cardozo and then talented 19-year-old Lazar Markovic were denied by Roberto.
The Spanish keeper joined the Greek champions on loan from Atletico Madrid during the close-season, but he played 41 times for his opponents in the 2010-11 campaign and was regarded as a flop before leaving for Real Zaragoza.
Jesus side dominated throughout and created numerous chances, but Roberto produced nine crucial saves and his old coach believes he finally proved to Benfica fans just how good he really is.
The 59-year-old said: We demonstrated, once again, the high quality of this Benfica team, we just could not translate our superiority into goals.
It is not normal for a goalkeeper to have so much influence on a game. Roberto was impeccable.
He saved six goals from us and he showed the quality I always saw in him.
The defeat in Piraeus meant Benfica remain on four points and stay third in Group C, while Olympiacos made second place their own by moving on to seven, but Jesus is still holding out hope for qualification behind leaders Paris Saint-Germain.
There are still two games left for us and for Olympiacos too, he added. This (loss) isn t decisive but they have an advantage over us.
Olympiacos almost had no shots except for the goal. I m not pleased because we didn t win but we showed again in Europe our quality.
Today we played great game. Today Benfica showed that even leaving with a draw would have been a bad result, given how we played.