Darren Way headed them into a lead before the break, with Kevin Gall sealing the 2-0 win after 87 minutes.
Crewe exited the competition in embarassing style - with a 5-1 drubbing at Lincoln.
Lee Beevers and Maheta Molango ensured the Imps had a 2-1 lead at the break, with Richard Walker netting for the Railwaymen.
But Gary Birch hit a quickfire second-half double, and Marvin Robinson sealing the win.
Northampton Town claimed an impressive 3-0 win over Queens Park Rangers.
Cheltenham cruised past League One leaders Brentford with a 5-0 win, after taking the lead through John Melligan just five minutes in.
But the goal glut didn't come until the second-half - with Grant McCann hitting a brace to couple with goals from Gavin Caines and Jamie Victory.
Nottingham Forest's poor start to the season continued with a 3-2 home loss to Macclesfield Town.
Sheffield Wednesday relied on an Adam Proudlock brace to see tham past Stockport in a dramatic period of extra-time.
The game was deadlocked at 1-1 after 90 minutes, with both sides scoring within a minute before Proudlock's late double intervention to seal a 4-2 win.
Barnet continued their acclimatisation to life back in the Football League win an impressive 4-2 win over a strong Bristol City side at Ashton Gate.
But their fellow League returnees Carlisle couldn't match that result, going down 2-1 at Burnley.
Blackpool claimed the scalp of Hull City. Shrewsbury beat Brighton 3-2, with substiute Jay Denny hitting two late goals to turn around what looked set to be a 2-1 loss.
First he sent the tie into extra-time with an 89th minute equaliser, then a minute into the added period he swept home Colin McCammon's cross to send the Shrews through.
Leicester eased past Bury 3-0, Crystal Palace beat Walsall 2-0 and Gillingham beat Oxford by a single goal.
Luton's strong start to the season continued with a 3-1 win at Leyton Orient, while Leeds saw off Oldham 2-0 at Elland Road.
Hartlepool ran out 3-1 victors in their north-east derby with Darlington, with Michael Proctor getting two of the goals.
Southend, who United host in the League on Friday, were beaten 3-0 by Southampton at Roots Hall on Tuesday night.
The Essex outfit had acquitted themselves well, but were sunk by strikes from Dexter Blackstock and Nathan Dyer within a minute of each other before half-time. Brett Ormerod added the third.
Shrimpers boss Steve Tilson said: "We paid the penalty for a couple of sloppy moments just before the break.
"You simply cannot afford to make mistakes against a quality side. You are always likely to get punished.
"But once they killed us off with those two goals just before the interval, it was all over. They killed the game in the second-half and never allowed us to get back into it."
Full results: Blackpool 2-1 Hull, Bristol City 2-4 Barnet, Burnley 2-1 Carlisle, Bury 0-3 Leicester, Cheltenham 5-0 Brentford, Crystal Palace 3-0 Walsall, Gillingham 1-0 Oxford Utd, Hartlepool 3-1 Darlington, Ipswich 0-2 Yeovil, Leeds 2-0 Oldham, Leyton Orient 1-3 Luton, Lincoln 5-1 Crewe, Mansfield 1-1 Stoke (Mansfield win 3-0 on pens), Millwall 2-0 Bristol Rovers, MK Dons 0-1 Norwich(AET), Northampton 3-0 QPR, Plymouth 2-1 Peterborough, Preston 0-1 Barnsley (AET), Reading 3-1 Swansea (AET), Rochdale 0-5 Bradford, Rotherham 3-1 Port Vale, Scunthorpe 2-1 Tranmere, Sheff Utd 1-0 Boston Utd, Shrewsbury 3-2 Brighton (AET), Stockport 2-4 Sheff Wed (AET), Swindon 1-3 Wycombe, Watford 3-1 Notts County, Wolves 5-1 Chester, Wrexham 0-1 Doncaster.
Wednesday night fixtures: Chesterfield v Huddersfield, Colchester v Cardiff, Derby v Grimsby, Rushden and Diamonds v Coventry, Torquay v Bournemouth
