Andy Carroll's 86th-minute header earned the Reds a victory over their local rivals at Wembley Stadium.
Despite the triumph, Cahill believes that Kenny Dalglish's team will find it difficult against Tottenham Hotspur or Chelsea.
"I think it's going to be difficult for them," he said. "They've had an indifferent season and they've just got away with it today.
"A few decisions didn't go our way but I'll just say they've got a lot of work to do."
Spurs take on Chelsea on Sunday for the right to play Liverpool in the final.