Last season's runners-up fell at the first hurdle this time and can have no complaints after the League Two side overcame the early setback of going behind to the Championship outfit.
It took just four minutes for new signing Heidar Helguson to get off the mark on his Cardiff debut.
The former QPR striker sent keeper Dean Snedker the wrong way from the penalty spot after defender Kelvin Langmead had been harshly penalised for impeding Helguson.
Northampton finally got back on level terms in the 37th minute when Ben Tozer's long throw-in found David Artell whose header beat the diving Joe Lewis and nestled in the bottom corner of the net.
The home side then took the lead three minutes after the restart when Lewis failed to deal with an inswinging corner from Ben Harding and Nicholls nipped in to head home at the far post.
Scunthorpe United beat Derby County 7-6 on penalties at Pride Park following an amazing 5-5 draw at Pride Park.
Derby had led 3-0 at half-time and were 5-3 in front going into stoppage time before late goals from , Connor Jennings and Bobby Grant (penalty) completed a stunning comeback to send the game into extra-time and ultimately penalties.
Plymouth scored twice in the last five minutes to ease past troubled League One club Portsmouth 3-0. Pompey boss Michael Appleton was forced to field nine teenagers in his starting XI as they continue to battle problems off the pitch.
Birmingham came from behind to comfortably see off Barnet 5-1 and book their place in the second round. Summer signing Jon Nurse headed the League Two visitors into a deserved lead and, after Marlon King equalised from the penalty spot. Steven Caldwell, Darren Ambrose Peter Lovenkrands and then Wade Elliott all scored in the second-half.
Swindon midfielder Alan Navarro scored just one goal in 73 appearances for Brighton but netted twice on his debut in a 3-0 win to stun Gus Poyet's side in the Capital One Cup.
Jamie Vardy, whose goals fired Fleetwood into the Football League last season, began to pay back his £1 million transfer fee with his first goal for Leicester as Nigel Pearson's Foxes cruised to 4-0 victory at League Two side Torquay.
Crystal Palace overcame brave resistance from Exeter before booking their place in the second round with a 2-1 win at St James' Park.
Paul Jones was Crawley's hero as the debutant goalkeeper helped his new side dump Millwall out of the Capital One Cup 4-1 on penalties after a 2-2 draw.
The loss of four players on international duty did not stop Burnley from marching into round two of the Capital One Cup with a 3-1 victory at League Two hosts Port Vale.
Charlton boss Chris Powell was sent to the stands barely an hour into the new season as his side tumbled out of the Capital One Cup 4-3 on penalties to Leyton Orient. Powell took exception to one of a number of meaty challenges in a fiery London derby which finished 1-1 after extra-time.
Ipswich survived a scare as they had to come from behind to progress beating Bristol Rovers 3-1 at Portman Road.
Manager Martin Allen got off to a winning start in charge of Gillingham as a goal in each half sunk Championship side Bristol City 2-1 at Ashton Gate.
Peterborough opened their campaign in fine style with a 4-0 hammering of League Two Southend at London Road. The hosts had the game won by the half-hour mark as a blistering start blew Southend away and gave them a 3-0 lead, which became 4-0 after the break.
Stevenage comfortably claimed a place in the second round with a 3-1 win over AFC Wimbledon in a match notable for a howler by Dons goalkeeper Seb Brown. Brown's air shot from a backpass in the 38th minute gave James Dunne a present and it also gave the League Two side a mountain they were unable to climb.
A dramatic extra-time strike by Abdulai Bell-Baggie put Tranmere through 2-1 in an incident-packed first-round tie at Chesterfield. The substitute pounced in the second minute of stoppage time after Cole Stockton had given the visitors a 94th-minute lead before Jack Lester levelled in the 109th minute.
Yeovil marched into the second round after a convincing 3-0 victory over Colchester. A brace from centre-back Richard Hinds and strike by Keanu Marsh-Brown ensured the Glovers secured their place in the next round.
Coventry boss Andy Thorn was able to breath a sigh of relief as his League One side scraped through into the second round by the skin of their teeth after a 1-0 win at Dagenham. League Two Dagenham looked to have to forced extra-time but they were stunned by a 90th-minute penalty strike from Kevin Kilbane as their cup hopes were ended at the first hurdle for a fifth successive season.
Oxford overcame League One Bournemouth on penalties after a goalless draw to continue the Cherries' poor run in the League Cup.