SOUTHAMPTON, England — Liverpool endured more cup frustration when Southampton won the first leg of their League Cup semifinal 1-0 on Wednesday.

Nathan Redmond capitalized on a mistake by Ragnar Klavan to score the only goal in the 20th minute and Southampton could rue not building a stronger lead to take to Anfield in two weeks' time.

"I should have had four today, on another day they might go in," Redmond told broadcaster Sky Sports.

"I'll take those mistakes and try to put it right in training and the next game."

Liverpool was struggling against a Premier League rival — unlike on Sunday, when fourth-tier side Plymouth drew 0-0 at Anfield in the FA Cup to force a replay.

Liverpool is competing for silverware on three fronts domestically in Juergen Klopp's first full season in charge, with Liverpool second in the Premier League and pursuing a first English title since 1990. Klopp guided Liverpool to the final last year but lost to Manchester City.

This week's difficulties in the cups have come ahead of one of the biggest games of the club's season on Sunday against northwest rival Manchester United in the league.

Southampton, which ended a four-match winless run, is in the last four of a major competition for the first time since 2003.

The hosts looked to be in for a bleak night, being forced to defend deeply in the opening stages and failing to find any real attacking outlets.

Jay Rodriguez was looking overwhelmed as Saints' focal point yet there was a flash of life in the 19th minute as Redmond collected a cross from the right and got away a shot that goalkeeper Loris Karius smothered well.

Redmond was caught out by the goalkeeper's reactions, but made amends within a minute as Klavan's inability to deal with a simple ball forward cost his side.

Rodriguez was alert to capitalize on the botched attempt to clear, beating former teammate Dejan Lovren with a deft pass to put Redmond through. This time, Redmond did not falter, keeping his composure to direct past Karius.

That blow after such a comfortable start threw Liverpool off kilter, with the visitors failing to attack with any intensity before halftime.

Southampton instead ended the opening period on top. Jordy Clasie saw an audacious attempt comfortably dealt with by Karius, who was a match for Redmond's close-range effort after collecting a Dusan Tadic cross just before the break.

The Serbian, signed as Adam Lallana's replacement in 2014 when the midfielder joined Liverpool, saw a threatening cross-shot cleared soon after play resumed, with Southampton pressing well and frustrating the visitors.

Daniel Sturridge's claim that he was upended in the box was ignored by referee Neil Swarbrick and Firmino saw a long-range effort stopped with ease, before Klopp turned to star man Philippe Coutinho.

Out since November 26 with an ankle injury, the Brazilian returned as a 61st-minute substitute in a bid to inspire the visiting side.

Coutinho was soon thrilling the raucous travelling support with his skill in winning a corner, but Southampton broke at speed when that set-piece came to nothing and looked set to score, only for right back Cedric to try his luck rather than cross.

Southampton continued to look the bigger danger but couldn't beat Karius again.