Five things we learned from Watford's superb comeback win against a misfiring Arsenal

Richarilson impresses for Watford, playing three at the back gives Per Mertesacker a role at Arsenal and Marco Silva should be very proud of this superb team performance

Watford and Arsenal played out an entertaining 1-1 draw (Getty)

Arsenal, who started without Alexis Sanchez and Mesut Ozil, failed to hold onto a first half lead but will ask questions of the referee as a controversial penalty for Watford made it 1-1 before the Hornets scored a late winner to snatch the three points.

Per Mertesacker gave Arsenal the lead on his first Premier League start for 532 days by taking advantage of Watford’s sloppy defending from a corner.

From then Arsenal failed to kick on and Troy Deny levelled the score line from the spot after

Watford were given a penalty when the referee, Neil Swarbrick, deemed Hector Bellerin to have fouled Richarlison who appeared to make the most of what little contact was present.

Late on Tom Cleverly completed the comeback by reacting quickest to a loose ball in the box to pile further misery on Arsene Wenger and Arsenal.

Here are five things we learned:

Three at the back gives Mertesacker a role at Arsenal

Mertesacker scored the first goal of the game (Getty)

Playing three at the back allows possession based teams, such as Arsenal, dynamism on the flanks, bodies in the middle and flexibility for attacking players.

What it also offers is a place in the side for Mertesacker, 33, who is retiring at the end of the season. The experienced defender is surprising his boss, and possibly himself, with every good performance in the middle of the back three. Beside him, Laurent Koscielny and Nacho Monreal hassle and chase defenders which allowsd Mertesacker to use his positional experience and anchor the back line.

He’s also fairly handy in the air too. No player in yellow got close to Mertesacker when he rose highest in the box and scored a header to give Arsenal the lead in the first half.

Marco Silva should be concerned by defensive frailties

Silva's side are fragile at the back (Getty)

Watford started the game know a win would take them to fourth place, so what’s the issue? The problem Marco Silva faces is that the goals conceded are sloppy and easily avoidable, similar to Liverpool’s defensive defects.

Only Crystal Palace, West Ham and Stoke have conceded more goals.

From a corner it was Tom Cleverly’s job to halt Mertesacker in his charge on the ball. 5 ‘ 9” Cleverly did not stand a chance against 6’ 6” Mertesacker who brushed his ‘marker’ aside and took advantage of Adrian Mariappa’s lackadaisical zonal marking at the front post.

Wenger successfully trials workmanlike side

Wenger arriving at Vicarage Road (Getty)

No Mesurt Ozil or Alexis Sanchez for the Gunners may have given an insight into the Arsenal side of next season.

Without a superstar, Wenger’s side returned to straightforward habits and relied on old fashioned hard work to secure three points and avoid another potential embarrassment.

Hector Bellerin, Sayed El Neny, Granit Xhaka and Sead Kolasinac could be the leading the way in a new industrious midfield as Wenger may have finally learned to adapt his style of play.

Richarilson is a very special player

Richarilson had a bright game for the home side (Getty)

Everything that Watford did well came through their unearthed gem, Richarilson. He started as a left winger by name only and occupied numerous positions on the pitch to maximise his involvement.

In the 70th minute, his quick turn of pace caught Bellerin off guard and he won his side a penalty. Replays suggest he went down fairly easily, not that the Watford fans will mind.

Ozil anonymous again

A number of Arsenal's high-profile names were left out the starting XI (Getty)

Wenger has been waxing lyrical about Ozil and insists that he makes Arsenal a much better side. He entered the action after an hour but did not drastically improve the team.

The World Cup winner continued to cut a frustrated figure and missed a great chance to put two nil up shortly before Watford equalised.