Northampton pulled off another cup upset as they knocked out Ipswich at Portman Road.
The Championship side took the lead when Jay Emmanuel-Thomas fired in from a tight angle.
But Northampton - who beat Liverpool last season - were level when midfielder Ben Tozer slotted home from close range after Arran Lee-Barrett had saved his initial effort.
Paul Turnbull grabbed the winner after Arron Davies saw his low shot blocked.
Gary Johnson's League Two side suffered a blow in the warm-up when striker Adebayo Akinfenwa picked up an injury, with Bas Savage drafted in as a late replacement.
Ipswich knocked the Cobblers out of the competition last season and Paul Jewell opted to rest the majority of the side that defeated Bristol City 3-0 on Saturday, with Aaron Cresswell and Emmanuel-Thomas the only players to keep their place.
His second string looked on track when Emmanuel-Thomas scored his first for the club with a cross-shot which evaded Sam Walker.
But Tozer struck after a neat exchange of passes with Jake Robinson before Turnbull took advantage of poor defending to score and put the Cobblers into round two.
VIEWS FROM THE DRESSING ROOM:
Ipswich Town manager Paul Jewell told BBC Radio Suffolk:
"I'm hugely disappointed that players we've given the opportunity to tonight to stake a claim for a first-team place didn't do as well as they should have done.
"I feel if [Michael] Chopra had been playing tonight we'd have won the game comfortably.
"We're desperately on the look-out for a centre-back, but like with every player we go for, it seems six or seven other clubs are also interested."
Northampton manager Gary Johnson told BBC Radio Northampton:
"The victory is very sweet because I thought we played really good football against a really good football team in Ipswich, who have that tradition.
"I did say I thought we could be part of a good match and as long as we showed commitment I thought our football would come out.
"They got their goal but the lads didn't fade and die and picked it up."