El Alagui broke the deadlock for the Bees just before the break, firing home Norris' left-wing cross on the half volley.
The hosts extended their lead straight after the restart, which brought three goals in a breathless six minutes.
Norris drilled home after a defence-splitting through ball from substitute Jake Reeves before El Alagui rounded the keeper to score from the tightest of angles.
But Wimbledon responded on 56 minutes when Fenlon smashed home a 20-yard screamer minutes after George Porter saw his goal-bound effort cleared off the line.
It was only a brief respite, with on-loan Cardiff defender Nugent powering home a header from Saunders' cross and ex-Villareal veteran Venta slotting home after Norris' close-range strike was blocked.
Wimbledon finished strongly, Francomb finishing a slick five-man move eight minutes from the end and Sweeney making it three when he converted Porter's low cross.
Wolves needed a penalty shoot-out to finally see off the challenge of local rivals Walsall after the game ended in a 2-2 draw after 90 minutes at Molineux.
Goalkeeper Aaron McCarey saved from Craig Westcarr and Andy Taylor as Wolves won the shoot-out 4-2 in the first meeting between the two neighbours for 10 years.
Wolves had twice taken the lead through Liam McAlinden and Bakary Sako only for Walsall to battle back through Ashley Hemmings and substitute Troy Hewitt.
Shaun Batt netted a hat-trick as League One pacesetters Leyton Orient cruised into the second round with a 3-1 victory at Gillingham.
Orient took the lead when Batt scored from the spot and he grabbed his second a minute before the break.
He slotted home a third before the hour and although Bradley Dack headed in a consolation for the hosts, Orient continued their impressive start to the season.
Previously goal-shy Hartlepool romped to their first win of the season as they thumped League One Bradford 5-0.
Pools had only scored one in six games going into the tie, but turned the hapless Bantams over with ease.
Goals from Luke James, Jon Franks, Christian Burgess, Jack Compton and Nialle Rodney helped them comfortably seal their progress.
Plymouth edged out League Two rivals Cheltenham on penalties after a six-goal encounter at the Abbey Business Stadium.
Cheltenham’s Terry Gornell's saw his spot kick saved with Plymouth scoring all five of theirs to progress to the second round, with Marvin Morgan hitting the decisive fifth.
Portsmouth also progressed on penalties following a 0-0 draw at Torquay.
Home skipper Lee Mansell fired Torquay's third penalty over the bar and the result was decided when Pompey right-back Yassin Moutaouakil successfully converted the visitors' fifth penalty.
And there was further drama from twelve yards as substitute Sean McGinty struck the winning spot-kick in a penalty shoot-out to steer Sheffield United to victory over Scunthorpe after a goalless draw.
The Blades won 5-3 on penalties after keeper Mark Howard had saved the third home spot-kick from Andy Welsh.
Brentford 5 – 3 Wimbledon
Dag & Red 4 – 1 Colchester
Gillingham 1 – 3 Leyton Orient
Hartlepool 5 – 0 Bradford
Tranmere 1 – 2 Fleetwood
Exeter 0 – 2 Wycombe
Port Vale 2 – 1 Bury
Crewe 1 – Accrington 0
Shrewsbury 1 – 4 Oldham
Cheltenham 3 – 3 Plymouth (Plymouth win on penalties)
MK Dons 2 – 0 Northampton
Notts County 1 – 0 Burton
Scunthorpe 0 – 0 Sheffield United (Sheffield United win on penalties)
Torquay 0 – 0 Portsmouth (Portsmouth win on penalties)
Wolves 2 – 2 Walsall (Wolves win on penalties)