A much-changed Liverpool side needed penalties to overcome League One Derby County after a goalless 90 minutes ended with the holders securing their place in the fourth round.
Jurgen Klopp made 11 alterations from the weekend's victory at Tottenham, and Derby held their own despite the 43-place disparity in league position.
The Rams' resistance made it all the way to the final whistle, but Caoimhin Kelleher saved three Derby penalties to see the Reds through.
Liverpool's escape keeps one of their best chances of silverware this season alive, with the Reds already 15 points behind Premier League leaders Arsenal.
Klopp's men dominated the early possession and Alex Oxlade-Chamberlain nearly gave them the lead after 15 minutes, but his powerful volley flew just wide after a corner was headed out to him.
The Reds continued to have the majority of the ball but they struggled to create clear-cut chances, as Derby sat back and made it difficult for the hosts.
The Rams' hard work was nearly undone before the break though, Layton Stewart latching onto centre-back Eiran Cashin's heavy touch before playing a one-two with Fabio Carvalho, though the young striker could only sidefoot well over.
Derby missed a great opportunity just after the break, Max Bird lashing wide after the ball fell kindly to him in the box before Joe Wildsmith was called into action, denying Oxlade-Chamberlain's deflected drive and then pushing away Carvalho's effort.
Klopp rang the changes to try force a way through, but the substitutions could not prevent the game going to penalties, despite Harvey Elliott and Roberto Firmino testing Wildsmith.
Wildsmith's opposing number Kelleher came up huge in the shootout to produce a trio of saves before Elliott stroked home to save Liverpool's blushes.
