The 18 year old along with another academy graduate Jay Spearing have made the transition into the first team.
"I wasn't surprised it didn't faze him," said the Scot of Flanagan's display.
"The development of him over the last year has been fantastic and that is the reward for him.
"Circumstances may have dictated that we pushed him in earlier than we would normally have done but he stood up to it and the good thing for him was he had Jamie Carragher beside him and Dirk Kuyt in front of him.
"The young boy is not bad. For us that is really encouraging as well because it is a reflection of the work that is being done at the academy and if we have a strong academy it can only benefit us in years to come."
Liverpool-born Flanagan admitted he was surprised to get his call-up in such a big game.
"It was a dream come true. I was told at quarter to six in the team meeting, it came straight out of the blue," he said.
"But Carra (Carragher) was telling me what to do and keeping my attention focused."