Mark Nwokeji made sure Dagenham's marvellous start to the season continued with a shock 1-0 Johnstone's Paint Trophy success at Peterborough.
Daggers boss John Still enjoyed a triumphant return to London Road by dumping out League One big spenders Posh - a team he managed for 18 months in the mid 1990s.
Nwokeji's 65th-minute header from a cross by substitute John Strevens was enough to settle this southern section second-round tie.
Mark Yeates' stunning second-half free-kick sent Colchester through to the next round with a 1-0 win which piled the pressure on Gillingham boss Mark Stimson.
Brighton clinched a place in the third round with a dramatic 5-4 win on penalties after Leyton Orient launched a spirited fightback to draw 2-2.
The Seagulls looked to be cruising after a penalty by Adam Virgo and a low shot from Joe Anyinsah put them two up after only 14 minutes, but Ryan Jarvis headed home in the 21st minute and Adam Boyd's 71st-minute penalty deservedly pulled Orient level.
Jarvis missed the opening penalty of the shoot-out and Robbie Savage also saw Brighton's first spot kick saved.
Orient were leading 3-2 on penalties when Virgo's kick was saved by rookie keeper Jamie Jones, but it was ordered to be retaken and Virgo scored.
Brighton squeezed through after Luke Ashworth's penalty was saved by Michel Kuipers and then Adam El-Abd stepped up to convert the decisive kick.
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