Liverpool manager Jurgen Klopp has admitted fielding an unpractised formation in the 2-1 win at Stoke City on Saturday.
Liverpool had to come from behind to win at the bet365 Stadium, with Philippe Coutinho and Roberto Firmino both needed from the bench to net second-half goals and secure the victory.
A switch to a 3-5-2 formation for the game seemed to provide instability to the visitors in a wretched first half in which they were lucky to go in at the break only trailing to Jon Walters' opener.
"The first half was actually not as good as we thought we could be,'' Klopp said. "We made a change to the system but we couldn't train it and that is what everyone could see -- everyone did not feel comfortable in the system.
"Defending was not a problem but we didn't defend like we normally do; we couldn't go high pressure. We saw we couldn't change the system in the second half, although we did a little bit offensively and created chances.''
Klopp's hand was forced at half-time and he removed teenagers Ben Woodburn and Trent Alexander-Arnold with Coutinho and Firmino coming on, even though the manager had decided with the sports science team before kick off both were only good for about 30 minutes' worth of football.
"You saw in the second half we were brilliant. Brilliant but for half-an-hour it was difficult,'' Klopp said. "It was not the plan to change twice at half-time. Offensive options were difficult because for Daniel [Sturridge playing from] half-time is really long in an intense game like this.
"I thought a lot about it and no one understands it but that was my decision. I thought we could have played much better than we did but it was clear bringing them on for half-an-hour made sense and they could decide the game.
"It was lucky for us because of the first half but it was deserved and we are completely happy and fine with this game.''
Liverpool were indebted to Simon Mignolet for two close-range saves, the first from Charlie Adam with the score at 1-0 and the second a brilliant far-post effort to deny Saido Berahino and hold on to their lead.
"This reaction is what you need to be successful,'' Klopp said. "You can't expect your goalkeeper to make saves like this each week but it was like scoring a goal.''