It was a day to remember for the travelling 8,500 Watford fans and here is how their team performed.
Defence rides their luck but holds firm for the majority of the game
Costel Pantillimon (7): Despite Arsenal's domination in the first half and wave of attacks at the end of the game, the 6 foot 8 inch goalkeeper did not have too many saves to make. When he was called into action he responded admirably.
Allan Nyom (6): The full-back was always in for a tough day against Alexis Sanchez but kept the Chilean relatively quiet with support from his central midfielders and defenders. Did not get forwards as often as he would like but did his job well.
Sebastian Prodl (7): The Austrian grew into the game and pulled off a number of important headers in the second half, although he will be concerned at how often he lost Olivier Giroud in the opening hour.
Craig Cathcart (8): What a difference having Cathcart back made to the Watford defence. Marshalled the troops excellently and was always willing to put his body on the line to block Arsenal shots inside and outside the box.
Nathan Ake (7): Continues to grow in confidence and managed to produce more of an attacking threat than Nyom, whilst also performing his defensive duties when required.
Energetic midfield display
Valon Behrami (7): Another player who made a huge difference on his return to the starting line-up, always willing to track runners and support Ighalo and Deeney in attack.
Ben Watson (7): Supported the defence well and was very disciplined with his approach to the game. As every defensive midfielder should be, he looked confident and composed on the ball, assisting Watford in making tracks into the Arsenal half.
Etienne Capoue (7): Still a bit sluggish in getting back to support the defence, but was always a willing runner in Watford's attacking moves and ready to support the strikers when his side broke forward.
Adlene Guedioura (8): Dangerous throughout the entire game, Guedioura scored a wonder goal to secure Watford's route to Wembley and deserved the accolades he got after the game.
Strikers back in synch
Troy Deeney (9): An inspirational performance from the captain. He held the ball up brilliantly for Guedioura's goal and flicked an assist for Ighalo's opener, whilst causing the Arsenal defence problems all day long with his determination. When Arsenal were attacking he always seemed to be back defending, supporting his midfielders and defenders excellently.
Odion Ighalo (8): The Nigerian's poor form of late continued in the first half as he struggled to get into the game, but he was a changed man when he grabbed his goal. It was like the Ighalo of old after he scored his first goal for 10 hours of football.
Ikechi Anya (6): Replaced Capoue on 73 minutes and added fresh legs to close down the Arsenal attacks.
Almen Abdi (6): Replaced Guedioura on 77 minutes producing a disciplined defensive display.
Nordin Amrabat (5): Replaced Ighalo on 82 minutes but could not use his pace and flair to push Watford further forward.