Matt Tootle's early goal stunned Crystal Palace before the Premier League side fought back to beat Shrewsbury Town.
Crystal Palace overcame a scare as they were forced to come from behind to beat Shrewsbury Town 4-1 after extra time and reach the third round of the League Cup.
Alan Pardew made nine changes to the side that beat Aston Villa in the Premier League on Saturday in order to "keep the squad alive".
That decision could have backfired as Matt Tootle's first goal for Shrewsbury since his move from Crewe Alexandra in June gave the League One side a shock early lead at Selhurst Park on Tuesday.
Dwight Gayle, one of the fringe players given his chance to impress, equalised from the penalty spot after Abu Ogogo upended Wilfried Zaha and also hit the crossbar just before the end of the 90 minutes as Palace were taken the distance.
Substitute Glenn Murray put Palace in front from 12 yards after he had been brought down by Mat Sadler, then Lee Chung-yong also struck early in extra time and Zaha got in on the act as Palace eventually secured their progress.
Patrick Bamford made his first Palace start as only Joel Ward and Zaha retained their places following the 2-1 victory over Aston Villa on Saturday.
Jean-Louis Akpa Akpro was one of three players recalled to the Shrewsbury starting line-up and the forward had a hand in an opening goal which stunned Palace just nine minutes in.
The Premier League side were caught out when Ryan Woods picked out Akpa Akpro, who in turn found Tootle and the right-back fired low into the far corner of the net.
Palace responded and the dangerous Zaha drove into the area, but was stopped in his tracks by some fine defending from Ogogo.
Ogogo had a moment to forget four minutes before the break, though, as he upended Zaha in the box and was punished when Gayle slotted home from the spot.
Bamford spurned a chance to open his Palace account when he fired over the crossbar after the lively Zaha had caused yet more problems for the Shrewsbury defence.
It was all one-way traffic as Zaha embarked on a brilliant late run before shooting wide and Shrewsbury goalkeeper Jayson Leutwiler kept out free-kicks from Lee and Gayle.
Gayle then struck crossbar from outside the penalty area with time running out to ensure Palace were taken to extra time, but Pardew's side made their superiority count in the extra half an hour.
Substitute Murray finished from the spot after Sadler had upended him in five minutes into extra time, then Lee cut inside his man and tucked home with his right foot two minutes later to give Palace a two-goal cushion.
Zaha then rose to head home Pape Souare's cross from the left four minutes from time and complete the scoring.