Palace won their Europa Conference League tie 3-0 thanks to goals from Christantus Uche, Eddie Nketiah and Yeremy Pino.
Advertisement
Advertisement
But O'Brien argued: "It's been massive.
"We'll do a deeper review after next week, but I think we'll look back to certain games where we were the stronger team, I felt, but missed big chances.
"They stuck at it, I'm proud of them. It's important to have that mindset when you're playing against a quality side and it leads onto next week, another big opportunity for us."
