Colchester won their first League Cup tie since 2010 after beating Swindon 3-0.
Swindon almost took a 12th-minute lead when U’s goalkeeper Dean Gerken made a fine stop to deny Jerry Yates from Keshi Anderson’s pass.
Anderson curled a shot over the bar and then fired into the side netting soon after, as the Robins threatened.
Gerken was called into action again early in the second period when he denied Anderson, who had exchanged passes with Scott Twine in the area.
Both sides were reduced to 10 men on the hour mark when U’s left-back Cohen Bramall and Swindon striker Yates were red carded, following an altercation on the touchline midway inside the U’s half.
But Colchester made the breakthrough with 13 minutes remaining through Tom Eastman, who emphatically fired in from Jevani Brown’s corner with 13 minutes remaining.
Gerken tipped substitute Lloyd Isgrove’s header away as Swindon piled on the pressure.
But substitute Courtney Senior slid in to convert Frank Nouble’s low cross from two yards in the second minute of time added on to make it 2-0.
And Brandon Comley then squeezed a shot over the line in the final seconds after Senior’s effort had been saved.