Alexis Mac Allister struck the only goal of the game as Liverpool won 1-0 on Tuesday night at Anfield.
Xabi said afterwards, "It was a demanding game, really fast-paced. We competed well but we lacked a real threat. The first half was fairly evenly matched and the second was decided by small margins. We started giving away too many free-kicks and the odd corner. Courtois kept us in it there. The goal gave them the edge and then we struggled a bit after that.
"I can't ask for any more from my team. We tried our best. It's the opening phase of the Champions League, we'll have chance to recover those points and we have to think about what's coming up.
“We have to learn that when they put the pressure on, which can happen when the crowd get up for it, we have to avoid giving away corners and free-kicks. We needed to create more opportunities. It was an intense game. We gave away a little bit too much at the start of the second half, we gifted them too many chances.
"It was avoidable. We should have been higher up, and they have great free-kick takers and finishers. They created a lot of chances because we gave away too many fouls."
Asked about the team's consistency, Xabi continued: “I don't think we're eratic. It wasn't a good performance at the Metropolitano but we have to be aware of the ideas we're putting across and the demands.
"Today was a really tough match and we have to be careful with those fouls because the game can get away from you, as happened today. We want to be consistent and I don't think we're eratic. It was evenly matched, hard-fought, and we can learn from this game."