Despite grabbing the only goal of the game in Eindhoven, Atletico Madrid's Saul belives his side's clean sheet was crucial.
"They pushed us back in the second period and it was difficult but we defended well – as we tend to do – and kept a clean sheet, which was really important," the 21-year-old midfielder told UEFA's official website.
"It was a great win and really hard fought – we know how important it is to win the first game in the group.
"We now have to carry on and think about the next game."
