Alexis Mac Allister struck the only goal of the game as Liverpool won 1-0 at Anfield.
Bellingham said afterwards: “I think the scoreline reflects the game, they were the slightly better side. They offered a bit more in the second half and were very dangerous from set-pieces. We didn't defend well enough. Courtois saved us a few times.
"I think we managed to find some space early on and we dominated for a spell in the first half. They had the edge in the second half and they won by the finest of margins. It's reflected in the result.
“It's still very early in the season and in the Champions League. We were far worse last season and we still made it through the first round. We can't let this game spoil the good energy and the positive atmosphere we've built. We'll focus on the positives, learn from the negatives and keep moving forward."
Teammate Fede Valverde added: “We came here to try and win the game, to take the 3 points. We know it's a really tough place to come, they really pile the pressure on. I think we had chances. In the end, we lost on a dead-ball situation when we should have defended it much better.
“There were three set-pieces in a row where they got headers on goal. We knew they were strong from set-pieces and we had to be stronger than them, defend better, with more desire and attitude."