Town boss Graeme Jones had declared his satisfaction at landing a rapid return to the Cardiff City Stadium little more than a fortnight since the Bluebirds pinched a 2-1 Championship win with a 95th-minute goal from former Hatter Isaac Vassell.
He made ten changes from the team that won at Barnsley on Saturday, and was rewarded with some fantastic football leading to a half-time advantage courtesy of an own goal from Junior Hoilett, before Sheehan's stunning free-kick just after the hour and Jervis' fine finish after striding through the heart of the City defence soon after.
Sheehan, back wearing the armband after summer surgery to repair his damaged achilles, and Jervis appearing on the scoresheet meant the Hatters have now had 11 different goalscorers so far this term - 12 including the own goal.
In goal was James Shea behind a back four of James Bree - Lloyd Jones, Sheehan and Brendan Galloway. Luke Berry, Pelly-Ruddock Mpanzu and George Moncur make up the midfield with forwards Elliot Lee, Jake Jervis and Izzy Brown ahead of them.
Shea was immediately involved, turning a left-footed drive from Omar Bogle around his near post with just over a minute on the clock. The same Bluebirds player was next to have a go, in the eighth minute, but his 20-yard effort following a quickly taken free-kick was too high to trouble the Town keeper.
The Hatters started to enjoy some decent possession, Bree progressing down the right and putting in a dangerous cross, but it was the hosts had the next attempt – Will Vaulks shooting straight at Shea – before Moncur curled the Town’s first shot high over the bar in the 15th minute.
Moncur danced his way into the Cardiff area in the 21st minute, but had the ball whipped off his toe before he could get his shot off. Junior Hoilett was soon firing at goal, however, but the left winger’s shot was well off target.
Berry was impressing in midfield, and he strode forward into the Cardiff penalty area to pick out Lee, whose volley on the turn was blocked behind by City skipper Aden Flint, their opening goalscorer in the league match earlier in the month.
Sheehan was enjoying himself, in his first appearance since Accrington away on East Saturday, and his clever interception ahead of Hoilett triggered a move that ended with Brown side-stepping a couple of men before unleashing a powerful 20-yarder that keeper Joe Day beat away.
Moncur was off-balance when he hit a wild shot from just outside the area soon after the half-hour, but the move that led to it, starting with Sheehan and Shea and involving a big switch to Bree and Jervis on the right, was a sign of the confidence now running through this Town team.
Hoilett and Isaac Vassell, the former Hatters striker who dealt the killer 95th-minute blow here just over a fortnight ago, were soon extending Shea again, then Jervis fired a left-footed shot well wide at the end of another good Town build-up.
The Hatters made the breakthrough two minutes before half-time, Lee picking out the run of Bree with a slide-rule pass to the right byline, and the Aston Villa loanee’s cut-back was deflected past his own keeper by the sliding, back-tracking Hoilett.
There was time before the half-time whistle for Jones to bring down Bogle as he bore down on the Town box, but Shea was once again behind Vaulks’ low shot, and the clean sheet remained intact.
Jones made one change at half-time, withdrawing Bree and bringing Bolton on in his place, while Cardiff replaced Vassell with Shamar Moore.
The first chance of the half fell to Berry, taking a throw from Bolton in his stride and firing over from a tight angle when a cut-back might have been more suited, before a Brown left-foot curler flew over the bar after intricate build-up play from Bolton and Lee set the Chelsea loan star up.
A long throw into the Town six-yard box caused a bit of concern in the 56th minute as Cardiff upped the ante, then Sheehan was at full stretch to intercept a dangerous-looking Hoilett cross a couple of yards from his own goal-line.
The captain was soon proving invaluable at the other end too, stepping up to whip a stunning 25-yard free-kick from the left of the penalty area around the defensive wall and into the top corner, leaving Day grasping at thin air.
Within seconds the Irishman was heading another dangerous-looking cross away, then he slid in to block a shot from Cardiff sub Gary Madine, who had capitalised on a loose ball and pulled the trigger from just inside the 18-yard box.
It was 3-0 by the 69th minute, and it was a first goal in a Hatters shirt for Jervis - more than 18 months after signing from Plymouth and having spent last season on loan at AFC Wimbledon - who produced a cool finish after racing through the middle and holding off a defender to latch onto a brilliant through-ball from Berry, deep inside his own half.
It was a great way for the forward to round off his first Hatters appearance since the first round of this competition a year and two weeks ago, with Callum McManaman coming on for him with just under ten minutes to go and the travelling Town fans giving him a terrific ovation as he made his way around the edge of the pitch in front of them.
The match also marked a first clean sheet of the campaign, with Shea rarely troubled late on as the Hatters await tomorrow night's draw to discover who they play in their first third round appearance in 12 years.
TOWN: Shea, Bree (Bolton 46), Jones, Sheehan (c), Galloway, Berry, Mpanzu, Moncur, Lee, Brown, Jervis (McManaman 82). Subs: Potts, Shinnie, Butterfield, Neufville, Stech.
Goals: Hoilett (OG) 43, Sheehan 63, Jervis 69
CITY: Day, Flint (c), Vaulks, Nelson, Paterson, Whyte (Waite 71), Brown, Coxe, Hoilett, Bogle (Madine 65), Vassell (Moore 46). Subs: Bennett, D'Almeida, Bodenham, Murphy (GK)
Yellows: Vaulks
REFEREE: Tony Harrington
ATT: 4,111 (232 Hatters)
