Plymouth Argyle ground out a goalless draw at Anfield to book an FA Cup third-round replay as the youngest team in Liverpool's history discovered they still have plenty to learn.
A Reds team containing five academy graduates came up against a green wall as Argyle manager Derek Adams succeeded in making life as difficult as possible for the hosts.
The tactics were understandable for a side second in League Two coming to a club second in the Premier League who score for fun at home, and Plymouth now have a chance of causing an upset at Home Park.
A replay is something Jurgen Klopp could have done without in a month which contains a two-legged EFL Cup semifinal against Southampton as well as a trip to Manchester United and the visit of league leaders Chelsea.
Chelsea beat Peterborough United 4-1 thanks to goals from Pedro, Michy Batshuayi and Willian, though they lost John Terry to a red card.
The Blues took the lead in the 18th minute when Peterborough goalkeeper Luke McGee could only parry Nathaniel Chalobah's shot and Pedro curled home the rebound into the top corner, before extending their advantage two minutes before the break when Batshuayi converted from close-range.
Willian added a third in the 52nd minute, scoring from Pedro's pass after good work by Cesc Fabregas.
Chelsea were reduced to 10 men in the 67th minute when Terry was sent off for a foul on Lee Angol and three minutes later Tom Nichols pulled a goal back for the visitors, tapping home from Angol's cross, but Pedro had the final word with a low effort into the corner after a neat one-two with Batshuayi.
Ben Davies and Son Heung-Min spared Tottenham Hotspur's blushes with two late goals in the 2-0 win over Aston Villa.
Mauricio Pochettino made nine changes from the team that ended Chelsea's 14-match winning run on Wednesday and his stand-ins struggled, until the 71st minute when Davies headed home his first goal in Tottenham's colours.
Son put the result beyond doubt with 10 minutes to play after Pochettino had brought on Dele Alli earlier in the second half to inject some life into his side.
Alli, who scored twice against Chelsea, certainly made a difference, along with 21-year-old winger Georges-Kevin Nkoudou, who came off the bench to set up Davies' opener.
Middlesbrough booked their place in the next round with a 3-0 victory over Sheffield Wednesday.
Grant Leadbitter opened the scoring for the hosts in the 58th minute, sending an excellent free kick into the bottom corner.
Boro were reduced to 10 men just a minute later when Daniel Ayala was shown a red card for a challenge on Fernando Forestieri, but Alvaro Negredo made sure of their spot in the fourth round when he charged down Joe Wildsmith to force the ball into the back of the net, with Marten de Roon scoring a third in injury time.
Ryan Sessegnon became one of the youngest goalscorers in FA Cup history with the winner in Fulham's 2-1 victory at Cardiff.
The 16-year-old tapped home from close range as Fulham came from behind to win, with Stefan Johansen having cancelled out Anthony Pilkington's deflected free-kick.
It was the second time Cardiff had witnessed the promise of the England under-17 international -- who was born in May 2000 -- as Sessegnon scored his first senior goal against them in August. On that occasion Sessegnon became the youngest scorer in both Championship and Fulham history at the age of 16 years and 94 days.
Five months on and Sessegnon showed his predatory instincts once more, even if Barrow's Sean Cato remains the youngest FA Cup goalscorer at the age of 16 years and 25 days.