Liverpool boss Brendan Rodgers admits they were fortunate to get away with victory over Champions League opponents Ludogorets.
Mario Balotelli's first goal for the club eight minutes from time looked to have won the game only for Ludogorets substitute Dani Abalo to roll in a 90th-minute equaliser for the Bulgarians.
However, captain Steven Gerrard scored an even later penalty after Javier Manquillo was brought down by goalkeeper Milan Borjan to ensure Liverpool's return to Europe's elite club competition after a five-year absence did not fall flat.
"It was very important to get back in the competition but it was always going to be a tricky tie for us because they are the champions of their country and there are not too many bad teams in the competition," Rodgers said.
"Maybe in the first six months we would have drawn and maybe even lost it but we showed the resilience and character in the group and, roared on by the supporters, it was great for us.
"We could do no more than win tonight. We are not at the standard we were last season, that is for sure.
"There is a lot of adaptation going on as we have a lot of players who have come in and are still adapting.
"We are a work in progress. While we do that it is important we win games.
"Tonight was about perseverance, an attribute you need to have, especially at the highest level.
"We kept going, kept pushing and the whole ground really appreciated that."
