The clash at Goodison Park got off to a slow start but absolutely burst into life after the break. Goals from Richarlison and Christian Kabasele put the visitors in control, but Everton fought back through Oumar Niasse, Dominic Calvert-Lewin and a penalty from Leighton Baines, and a missed penalty from Tom Cleverley in the final minute ensured the three points for the Toffees.
Watford were dominating possession but neither side created clear-cut chances in the opening stages with a number of overhit crosses for Watford coming from Andre Carrillo and Tom Cleverley.
Kiko Femenia was lively down the right flank and forced Wayne Rooney to provide defensive cover for Leighton Baines. The Spaniard played a few dangerous balls into the box but Andre Gray and Richarlison weren’t able to connect with them.
The first real chance of the game fell to Everton just after 20 minutes. Wayne Rooney cut the ball across the box for Leighton Baines, who had plenty of time to shoot, but his side-footed effort was parried by Heurelho Gomes.
Towards the end of the half Watford started to dominate and they should have taken the lead five minutes before the break. Richarlison was slipped through by Andre Gray for a one-on-one with Jordan Pickford and he took the ball past the onrushing goalkeeper but then hit the side netting from a tight angle.
Moments later, Jose Holebas’ blocked shot fell to Abdoulaye Doucoure on the edge of the area and the Frenchman hit a clean strike goalwards, but Pickford kept the effort out well.
The sides went in level at half-time and although it was an even first 45 minutes, the visitors will have felt disappointed not to be ahead.
To say the second half exploded into life would be an understatement.
Within 30 seconds of the restart, Richarlison had made up for his earlier miss and gave Watford the lead. On a counter attack, Gray dinked the ball across for Richarlison on the left, and the Brazilian rounded Pickford and finished cooly inside the near post to make it 1-0.
Heurelho Gomes made a superb double save after 53 minutes as he denied Sigurdsson from close range before recovering punch out a cross from Rooney, but he was injured in the process and had to be replaced by Orestis Karnezis in the Watford goa.
10 minutes later, the Hornets deservedly extended their lead. Holebas whipped a brilliant corner into the box and Kabasele simply rose to nod the ball into the bottom corner.
Marco Silva’s side were cruising and looked the most likely to get the next goal, but just three minutes later Everton had a route back into the game.
Karnezis, who was making his Watford debut, got in a terrible mix-up with Holebas and Niasse took full advantage after chasing a seemingly dead ball to tap the ball into the net to make it 2-1 after 67 minutes.
After the goal Everton had the wind in their sails and were determined to find an equaliser, and they found it just seven minutes later through Dominic Calvert-Lewin. The youngster had come off the bench and headed home at the back post from a Leighton Baines corner to level the scores.
The game could have gone either way with both sides pushing for the winner in the latter stages and Adrian Mariappa headed inches wide from another Holebas corner.
However, in the 88th minute it was Everton who completed the turnaround from the penalty spot. Holebas can consider himself unlucky as he lost his footing to bring down Aaron Lennon inside the box, and Baines made no mistake firing past Karnezis from 12 yards.
The game was far from won for the Toffees as there were 12 minutes of additional time following lengthy stoppages for injuries to Gomes and Kabasele for the away side.
Indeed, it looked as if Watford would take full advantage of the lengthy stoppage time when Richarlison was brought down by Pickford inside the area in the 99th minute.
Tom Cleverley stepped up against his former side but his awful penalty was dragged several wides yard of the post and Everton held on for a memorable victory.
The win takes Everton out of the relegation zone and into 15th place, as David Unsworth tries to prove his worth as a possible candidate for the permanent manager’s job at Goodison Park.
Meanwhile, Marco Silva’s side have now lost three consecutive Premier League games and will be bitterly disappointed with the nature of the result, especially after such a positive start to the season.