Watford have fallen at their first hurdle in the League Cup to lower league opposition for the second season running, but this time in their own back yard as they were humbled by League One Gillingham 2-1 following extra-time on a highly unsatisfactory night for the Hornets at Vicarage Road.

Walter Mazzarri’s men had sufficient chances to have their place in the next round secured by half-time, but their failure to make the breakthrough didn’t look like it would cost them when Odion Ighalo scored shortly after coming off the bench.

But much of the Hornets’ attacking impetus went when Matej Vydra was replaced and after the Hornets had survived a warning when Bradley Dack missed a penalty, they increasingly retreated into their shell and could have few complaints about being pegged back.

And it was to get worse for the hosts in extra-time as a couple of tepid half-chances came and went before Dack completed the upset just before the interval of the additional 30 minutes as the Gills showed no signs of tiredness and their hunger shone through.

Watford had started relatively brightly with Vydra looking busy and sharp, but after Troy Deeney and Ikechi Anya had been thwarted by goalkeeper Stuart Nelson the Hornets started to lose their attacking way and the quality of the remainder of the first half descended as a result.

But the Hornets were out early for the second half and after Mazzarri had decided to shake things up early on by introducing Ighalo, the move paid instant dividends as the substitute netted his first of the season.

Ighalo and Tommie Hoban both went close to making the tie safe, but Watford’s inability to convert more of their chances meant they were always susceptible and Gillingham should have levelled when Allan Nyom needlessly brought down substitute Elliot List in the penalty area, only for fellow substitute Dack to blast horribly over from 12 yards.

But Watford did not heed the warning signs and, like against Chelsea on Saturday, increasingly went into protection mode and they paid the price with eight minutes of normal time when Mark Byrne curled a fine, low 25-yard shot beyond Costel Pantilimon.

Extra-time brought no real improvement in performance from the home side and they were facing embarrassment at the turnaround in extra-time after Dack made up for his penalty miss by giving the Gills the lead, which they were to held onto with relative ease in the end to send their small army of fans back to Kent delighted.

Mazzarri, as expected, made wholesale changes from the side that that lost late on against Chelsea on Saturday with only Adlene Guedioura and Troy Deeney retaining their places.

The captain was reunited with Vydra up front in as a Hornets strike pairing for the first time since the final day of the promotion-winning 2014/15 season, while Tommie Hoban came in for his first appearance at first-team level since April of that campaign.

There was a debut for Christian Kabasele, Juan Carlos Paredes came in having not featured at all in the first two league games but perhaps surprisingly, Mazzarri decided against giving a first start to Younes Kaboul following his arrival from Sunderland on Friday. But the centre-half was on a bench that also included former Tottenham Hotspur teammates Heurelho Gomes and Etienne Capoue, who was fit to be included after being taken off with an injury at the weekend, while Nordin Amrabat, Valon Behrami, Miguel Britos, Craig Cathcart and Sebastian Prodl were given the night off.

Gillingham had been enjoying an unbeaten start to the League One season but came a cropper on Saturday when they were thumped 5-0 at Scunthorpe United.

Boss Justin Edinburgh resisted any temptation to make significant changes though, making just the one with Cody McDonald coming in for Rory Donnelly.

The Gills matched their opponents to an extent by going with three at the back, but it was the hosts who sought to impose themselves on proceedings from the outset, with Deeney showing a willingness to drop deeper early on to provide a link between midfield and attack.

And it was the captain who almost gave his side a sixth-minute leading, forcing Nelson to parry Deeney’s firmly-struck side-footed effort after the ball had been pulled back to him by Anya.

A second good opening came for the hosts seven minutes later when Abdoulaye Doucoure’s cross-field pass ball from right to left was latched onto by Vydra on the left side of the area and he then proceeded to produce a lovely back-heeled lay-off to set up Anya, but the Scotland international saw his attempted finish blocked by Nelson.

The Gills’ first sight of goal came soon after when after play had been recycled following a corner, McDonald head harmlessly over Costel Pantilimon’s goal.

The hosts continued to play some nice stuff at times but the quality wasn’t there when it was required and some of their initial attacking verve dissipated as the opening 30 minutes ticked by.

But Nelson was called into action again in the 32nd minute to keep out another Anya effort after the Scotland international had worked a one-two with Deeney to create the space on the left side of the 18-yard box. But the ball was only cleared as far as Doucoure on the edge of the area, he had time to watch it drop onto his right foot but volleyed wide.

The Hornets were almost in again when Deeney capitalised on a hopeful long ball forward by Paredes to head on and cause confusion in the Gills’ defensive ranks, but Nelson managed to get there just before Vydra, although he clattered into teammate Josh Pask in the process.

The Gills had by no means come to just defend though, and they won a couple of corners before Guedioura opted to take aim from 30 yards and fizz a trademark right-footed narrowly drive just wide.

Watford’s sporadic pressure continued with Nyom getting to the byline and pulling the ball right across the six-yard area, but no teammate was in the right place to apply a killer touch as a goalless first period drifted to a close.

The Hornets were on the front foot from the restart, with Anya seeing plenty of the ball down the left, and from one of his balls into the box the ball was recycled to Ben Watson, who sent a rising drive a yard over from the edge of the 18-yard box.

It looked like a first goal for the home sight might arrive in the 52nd minute when Anya played the ball into the near post and Deeney slid in, but Deji Oshilaja went with him and managed to shepherd the ball back to Nelson after it seemed to get stuck beneath the defender’s body.

Mazzarri decided to shake things up in the 55th minute by bringing on Ighalo for Guedioura and within two minutes the change had paid off.

Deeney started the business end of the move off by clipping the ball over the top to the substitute, who was given a second bite at the cherry after Nelson had blocked his initial effort before calmly rolling the ball over the line to make it 1-0.

Ighalo almost had a second when he was set up by Vydra after a nice passing ended with the Nigerian international’s shot being deflected behind.

Before the corner was taken though, Mazzarri brought on Capoue for Vydra, who was afforded a loud ovation as he left the pitch and the striker responded in kind by applauding the Hornets fans in kind.

The Gills boss also took the opportunity to make a couple of changes but when play did restart from the set piece, the Hornets were very close to going 2-0 up when Hoban’s effort was parried and deflected onto the underside of the bar before it was hacked to safety.

But instead of going two goals to the good, Watford were very fortunate not to be pegged back to 1-1 when Nyom needlessly brought down substitute List on the left side of the penalty area, but the defender was reprieved by a shocking penalty from Gillingham’s other replacement, Dack, who blasted wildly over.

Following that escape, the home side looked to assert themselves in the opposition half again and Nelson had to save smartly to keep out a Deeney header. But it was the visitors who were coming on the stronger and after their third substitute Darren Oldaker had forced the back-tracking Hoban to repel his shot, the Gills levelled in fine fashion when Byrne cut in and curled a superb low left-footed shot from 25 yards into the far corner past Pantilimon.

Boosted by the equaliser, Gillingham were the more composed side as they went in search of a late winner, with Emmanuel Osadebe firing straight at Pantilimon from 20 yards.

The flag was already up for offside when Hoban went very close from a free-kick into injury-time, but neither side were able to find a winner inside the 90 minutes.

Ighalo wasn’t too far wide with a drive from the edge of the 18-yard box before Juan Camilo Zuniga came on for Anya. And it was the replacement who was to have the Hornets’ next effort, cutting in off the left before shooting wide of the near post.

But what had a been an increasingly disappointing night for the Hornets got significantly worse three minutes before the interval when Osadebe’s fine cross from the right was met by Dack. Although Pantilimon managed to get a hand to it to help the ball onto the post, he was unable to keep it out, although referee James Linington did consult the goalline technology before awarding the goal.

The hosts finally began to show a measure of urgency after the resumption and four minutes into the second period Hoban was again thwarted by Nelson following Zuniga’s low delivery in from the left.

The Hornets continued to press with crosses coming in from various angles but as with much of what had gone before, the quality wasn’t there as Mazzarri’s men continued to huff and puff against a Gilld side holding its shape well and that deservedly secured their progress through to the next round of the competition while their opponents could have no complaints at being booed off after the final whistle.

Watford: Pantilimon; Nyom, Hoban, Kabasele; Paredes, Guedioura (Ighalo 55), Watson, Doucoure, Anya (Zuniga 94); Deeney, Vydra (Capoue 65). Not used: Gomes, Kaboul, Sinclair, Holebas.

Gillingham: Nelson; Ehmer, Pask, Oshilaja; Osadebe, Byrne, Wright (Oldaker 74), Konchesky (List 65); Knott; Emmanuel-Thomas (Dack 65), McDonald. Not used: Hadler, Hessenthaler, Donnelly, Dickenson.

Bookings: Byrne for dissent (118).

Attendance: 7,004.

Referee: James Linington.