Heading to Portugal with a 1-0 lead from the first leg, the Reds dominated Porto at the Estadio do Dragao last night.
Sadio Mane, Mohamed Salah, Roberto Firmino and Virgil van Dijk were the scorers for Liverpool as Eder Militao pulled one back for the hosts.
Their reward will be a trip to the Nou Camp to take on Messi, Luis Suarez and co, after the Catalan giants dismantled Manchester United on Tuesday.
The Argentine scored the opening two goals on the night before former Red Philippe Coutinho’s screamer in the second half completed the rout.
Barca progressed 4-0 on aggregate, progressing to the semi finals for the first time since 2015.
The two games will be played on April 30 and May 7, and Liverpool will travel to Catalunya first.
After the win was sealed, Klopp discussed how to deal with Messi, and gave an admission that could be alarming for Reds fans.
“Thank God I don’t have to think about that tonight,” he said.
“I have a few nights. Nobody has managed it, but we will try.
“We have a few jobs to do before that.”
Klopp and Liverpool stand on the verge of an unprecedented season for the Merseyside club.
Not since 1984 have the Reds completed a league and European cup double, but they will have few chances like they do this year.
With four Premier League games remaining, Klopp’s side are sat atop the Premier League by two points from second-placed Manchester City, who have a game in hand.
Their run-in is considered to be much kinder than City’s, however, as they will play already-relegated Huddersfield, relegation-threatened Cardiff, before a trip to Newcastle and a final home game against Wolves.
City, on the other hand, will have to play Tottenham Hotspur on Saturday – the third time they will have faced the North London side in 12 days – before a trip across town to face Manchester United.