Premier League sides Watford and West Brom crashed out of the League Cup after suffering disappointing defeats to lower-league opposition on Tuesday.
League One side Gillingham pulled off an upset 2-1 victory at Watford, with Bradley Dack scoring an injury-time winner at Vicarage Road to send his team into the third round.
Zander Diamond gave Northampton Town of League One the lead at home to West Brom, but James McClean and Gareth McAuley seemed to have put the Premier League side in control of the tie.
An equaliser by Alex Revell with just eight minutes to go forced extra-time and, after no goals in the added 30 minutes, penalties were needed to decide the winner.
Saido Berahino and James Morrison missed from 12 yards for West Brom, with Kenji Gorre stepping up to convert his kick and book a third round place for the underdogs.
The other seven Premier League teams made it safely into the next round of the competition, with Liverpool winning 5-0 at Burton Albion and Chelsea survived a scare by beating Bristol Rovers 3-2 at Stamford Bridge.
There was almost another shock at the iPro Stadium as Championship side Derby County triumphed 14-13 in a marathon penalty shootout to knock out Carlisle United of League Two after a 1-1 draw.