Jürgen Klopp felt that some of his younger players were worried about being “embarrassed” by lower-league opponents during the first half of Liverpool’s narrow FA Cup third-round replay victory against Plymouth Argyle, although the German maintained that he picked the right team on a night when Lucas Leiva scored for the first time in more than six years.

FA Cup fourth round draw • Blackburn Rovers v Blackpool • Burnley v Bristol City • Chelsea v Brentford • Crystal Palace v Manchester City • Derby County v Leicester City • Fulham v Hull City • Lincoln City v Brighton & Hove Albion • Liverpool v Wolves • Manchester United v Wigan Athletic • Middlesbrough v Accrington Stanley • Millwall v Watford • Southampton v Arsenal • Oxford United v Newcastle United • Rochdale v Huddersfield Town • Sutton United v Leeds United • Tottenham Hotspur v Wycombe Wanderers Ties to be played 27-29 January

The Liverpool manager said he would have been “a real idiot” if he had selected more first-team regulars, given the club’s schedule over the next couple of weeks, with Swansea City’s visit to Anfield on Saturday the first of four matches in the space of 11 days, including the EFL Cup semi-final second leg against Southampton on Wednesday and the Premier League visit of the leaders Chelsea on 31 January.

Liverpool can now also look forward to an FA Cup fourth-round tie at home against Wolverhampton Wanderers on Saturday week after Plymouth were beaten 1-0 on the south coast. Divock Origi missed a late penalty for Liverpool, but the Premier League club endured some nervous moments before that, in particular when Jake Jervis struck an upright with an acrobatic volley in the 75th minute.

“It was tough,” Klopp said. “We had a lot of young players today and one of the challenges they had was playing live on television against a fourth division team and everyone thinks you are three-to-four classes better, and then not feeling embarrassment when you lose a challenge or something. I really saw it in the first half when it started happening to them.

“At half‑time we could fix this a little bit, so we were kind of back in the race, controlled the game. But they [Plymouth] did really well. They had one or two chances, two or three more difficult situations, but I heard the biggest chance was offside. We had more chances and the penalty, so two or three-nil would have been completely OK and the perfect result. But 1-0 is also good.”

Although Klopp gave Philippe Coutinho his first start since November and Daniel Sturridge was also in the XI alongside Origi, the Liverpool manager had four teenagers on his team-sheet. “I named the team I could name, that’s what I always do,” Klopp said. “Only you [the media] judge it as stronger or weaker, I don’t do this. It’s all about who is available. We play now Saturday, then Wednesday, then Saturday, then Tuesday. If I always let the same players play I would be a real idiot. So I don’t do it.”

Klopp was full of praise for Lucas, whom he is determined to hold on to this month. The Brazilian’s goal was his first since he scored against Steaua Bucharest in the Europa League in September 2010, when Roy Hodgson was Liverpool manager. “A great personality, a good player, a really wonderful guy,” Klopp said. “We play old against young in the last training session before the game, and Lucas is top scorer of the old team so I am really surprised he didn’t score for that long. But now he’s back on track.”