All Premier League teams survived unscathed in the second round of the Carling Cup although violence inside and outside of Upton Park marred West Ham's 3-1 win over Millwall.
Wolves went through 6-5 on penalties against Swindon after a 0-0 draw at Molineux.
Adam Boyd put the League One outfit in front on 39 minutes, but Fletcher equalised late on and then hit the winner in extra time.
The Saints went ahead through Adam Lallana on 51 minutes, but two late strikes from Lee Bowyer and Lee Carsley proved decisive.
Tom Cairney and Jozy Altidore scored debut goals for Hull and Geovanni added a third in the 3-1 defeat of Southend.
Franck Moussa notched Southend's consolation.
Blackburn also overcame League One opposition, 3-1 at Priestfield over Gillingham.
David Dunn's settled the nerves with an early strike and David Hoilett and Morten Gamst Pedersen scored either side of Simeon Jackson's penalty.
Troubled Portsmouth coasted to a 4-1 home win over Hereford.
Frederic Piquionne's first goal for Pompey broke the deadlock and John Utaka, Niko Kranjcar and Richard Hughes were also on target before Tristan Plummer scored a consolation from the penalty spot.