Watford are at Wembley. The Hornets are one game away from their second appearance in an FA Cup final after a stirring second-half display was rewarded with a 2-1 win at Arsenal to end the Gunners’ two-year grip on the trophy.

The Hornets had ridden their luck at times in the first half but once Odion Ighalo put his side in front six minutes after the break, everything changed.

The Gunners increasingly began to struggle after their fragile confidence had taken another blow while their opponents looked increasingly confident on the counter attack.

But few would have predicted the manner of the visitors’ second goal when it did arrive – a simply stunning right-footed drive from Adlene Guedioura that arrowed into the roof of the net.

A Danny Welbeck goal gave the home side late hope and the England striker almost secured a replay when he sent a great chance wide at the death after Alex Iwobi had hit the post, but the Hornets held out to secure a famous win and send more than 8,000 fans into collective ecstacy.

Both sides were listed as making three changes from their last games but Quique Sanchez Flores threw in what initially appeared to be a couple of curve balls as Watford reverted back to 4-2-3-1 to match up Arsenal’s shape.

Having stated Costel Pantilimon would start in goal, there was a surprise when the name of Heurelho Gomes appeared on the teamsheet, while the other unexpected inclusion was Guedioura in the attacking midfield three. The other changes saw the fit-again Craig Cathcart return and Valon Behrami picked in the engine room.

That meant Mario Suarez and Nordin Amrabat dropped to a bench that included the fit-again Jose Manuel Jurado amidst a wealth of offensive options, but Jose Holebas missed out completely having started the 1-0 defeat to Leicester City.

However, it transpired Pantilimon had been selected all along, with BT Sport reporting Gomes’ inclusion in the starting line-up had been due to a pre-match administrative error.

With a Champions League trip to Barcelona looming large on Wednesday, the question in the build-up to the game was how strong a side Arsene Wenger would select. The inclusion of Mesut Ozil and Alexis Sanchez said everything.

Francis Coquelin also came back into the Gunners’ starting XI as Mathieu Flamini, Theo Walcott and Iwobi made way from the side that began Tuesday’s fifth round replay win at Hull City.

The hosts had plenty of the ball from the outset and created the first opening inside three minutes when Sanchez dropped deep to pick up possession and switched play to the right where Joel Campbell fed the overlapping Calum Chambers, but nobody in a red or white shirt was able to get on the end of his ball across the six-yard box.

The Gunners continued to dominate the early exchanges and the Hornets were saved by an offside flag in the 11th minute when, after Ben Watson had been caught in possession, the ball was played up to Sanchez, who in turn fed Olivier Giroud and he slipped a low finish past Pantilimon but Arsenal’s celebrations were quickly curtailed.

Following that scare though, the Hornets had their first moments of attacking promise as Behrami and Ighalo made some inroads into the 18-yard box.

But Watford safely negotiated their way through the opening 20 minutes of a game that was relatively scrappy with the home side continuing to have most of the ball, but twith both sides being guilty of giving it away at times.

However, the visitors could, and perhaps should have been in when a delicious pass from Etienne Capoue with the outside of his left boot set Ighalo away down the inside left channel. He teased Per Mertesacker in the penalty area but opted to try and find Troy Deeney instead of shooting, but the pass lacked accuracy.

Deeney then required treatment when he went for a 50/50 challenge with Gabriel in which the Arsenal defender clearly missed the ball as he slid in and caught the Watford skipper flush on the shin, but referee Andre Marriner somehow deemed it to be a fair challenge. It looked a poor decision by the official in real time but subsequent replays showed he’d got it very wrong.

The Hornets escaped a second let off 15 minutes before the break when after a corner had been partially cleared, the ball was played back to the right side of the area where Mohamed Elneny had the time to bring it down and pick his spot, only to blaze over.

Watford were soon countering again though, again it was Ighalo who led the charge and again his pass selection let him down when he tried to find Deeney on the right side of the penalty area instead of taking it on him himself.

Most of the attacking questions continued to be asked by the home side and four minutes before the break Elneny spurned another great opportunity to give Arsenal the lead, this time blazing over from the edge of the 18-yard box after being fed by Campbell following a delightful piece of skill from Ozil which had taken him away from Nathan Ake near the byline.

The Gunners continued to turn up the heat before the interval with Campbell lifting the ball over Pantilimon and the bar after a slip by Ake had put him through on goal to latch onto an Ozil pass and then the Hornets keeper picked up the game’s first yellow card for time wasting in Marriner’s eyes.

But Watford managed to keep it goalless until the break, although they had been second best for the most part of the opening period.

Arsenal’s first chance of the second half came within 90 seconds of the resumption when Ozil swung over a corner from the left and Giroud was able to pull off into space around 12 yards out in the near post region but he headed over.

Watford had yet to have a shot on target but that all changed - and then some - in the 51st minute when a quarter of the Emirates Stadium was sent into collective delirium.

It originated from a long throw on the left which Deeney was able to lay off to Ighalo, who with his back to goal turned and fired a right-footed finish beyond David Ospina to put the Hornets 1-0 up.

Having ended a goal drought that dated back more than a month to the Hornets’ fourth round win at Nottingham Forest, Ighalo wasn’t too far away from doubling his tally soon after when he volleyed over after more good work from Deeney to head a deep Allan Nyom cross back into the danger zone.

Arsenal’s first response to falling behind came from Elneney as he hit a stinging 25-yard drive straight at Pantilimon. But their opponents were looking a real threat on the counter and on the hour Deeney set Ake away in the inside left channel and he delivered a dangerous ball across the six-yard area which Ighalo just wasn’t able to get his foot around.

It was already looking good for Watford but on 64 minutes they took complete control thanks to a simply brilliant second goal.

Again it originated from a counter attack with Ighalo feeding Deeney on the right side of the six-yard box and the Hornets captain did very well to hold the ball up before laying it back to Guedioura who, without breaking stride, hit an absolute rocket of a right-footed drive on the angle that flew inside the helpless Ospina’s near post to put the visitors two goals to the good.

Giroud and Sanchez both had half chances before Wenger opted to play all his cards at once, bringing on Iwobi, Welbeck and Walcott for Elneny, Campbell and Giroud after 66 minutes.

Flores followed suit seven minutes later as Ikechi Anya replaced Capoue but the Hornets were still looking in control and defending resolutely when necessary.

After goal scoring hero Guedioura had been replaced by Almen Abdi, the Gunners continued to knock at the door but again Pantilimon wasn’t unduly extended in saving a Kieran Gibbs header following a pull back from the right.

Ighalo’s afternoon came to an end with nine minutes remaining when he limped off and was replaced by Amrabat before Chambers flashed a shot across the face of goal and wide after being picked out by Sanchez.

The Hornets might have added a third with four minutes remaining when Deeney set Anya away in the area, but he was unable to get the ball past the outstretched leg of Ospina as he tried to feed Amrabat.

But with just over two minutes of normal time remaining Watford’s defence was finally unpicked. Sanchez played the ball to Welbeck, who laid it off to Ozil as the striker continued his run into the area. Arsenal’s assist king this season added another to his collection with a lovely back heel to return the ball to the England forward and Welbeck placed the finish across Pantilimon to make it 2-1.

The Hornets’ resolve now faced a stern examination but they needed a big slice of good fortune to prevent the Gunners from equalising when an Iwobi shot from the edge of the area hit Pantilimon’s right-hand post and struck the Hornets’ keeper before running loose. The hosts then managed to work the back to Welbeck, who appeared to have a formality finish, even though the ball was behind him, but he lifted the ball wide of the target. With that chance went Arsenal’s grip on the FA Cup.

Arsenal: Ospina; Chambers, Mertesacker, Gabriel, Gibbs; Elneny (Iwobi 66), Coquelin; Campbell (Welbeck 66), Ozil, Sanchez; Giroud (Walcott 66). Not used: Macey, Monreal, Flamini, Bellerin.

Watford: Pantilimon; Nyom, Prodl, Cathcart, Ake; Watson, Behrami; Capoue (Anya 74), Deeney, Guedioura (Abdi 77); Ighalo (Amrabat). Not used: Gomes, Suarez, Jurado, Oulare.

Bookings: Pantilimon for time wasting (43); Ozil for a foul on Behrami (74).

Attendance: 58,436 (8,247 away fans).

Referee: Andre Marriner.