An own goal by Watford centre-back Craig Cathcart gave the Gunners the lead before Mesut Ozil, notably quiet for most of the match, fired home from Alexandre Lacazette's cross.
"He's told me to stop being so critical and to just keep trying no matter what happens, no matter if things don't go as I want them to".
But the Welshman was largely ineffectual, and even when he was given the captains armband after Cech's injury he didn't improve and he was finally hauled off by Emery and replaced by Alex Iwobi.
However, the 36-year-old failed to complete the ninety minutes as Cech was forced off just before half time after pulling up with a hamstring injury while taking a routine goal kick in first half stoppage time.
With Arsenal under the cosh in the second half, Leno made a fine save to deny Troy Deeney and coped well under the Watford bombardment.
Emery also needs to resolve the tricky issue of Aaron Ramsey's future.
"They are a team with very good players, very competitive and with the duels they are a very hard team".
Ramsey has started all-but one of the six Premier League games under Emery's tenure but the Spaniard insists his only focus in the role of head coach is preparing the team.
"But we know, tomorrow we need to play and we need also in the individual duels on the pitch, to win for step-by-step in the 90 minutes so we can impose our ideas, our job and our moment physically on the pitch".
Zielinski has always been tipped to move to the Premier League, with Liverpool chasing the Poland worldwide before he joined Napoli in 2016 from Udinese. We need to continue to be calm.
Ozil has been in impressive form of late with two goals from his last three games.
"What can I say?" he lamented.
"I want him to stay nearer the box to score and be more aggressive, finding assists for team-mates".
The Ramsey situation is yet another example of Arsenal's ineptitude in dealing with expiring contracts within their squad, and they have repeatedly left themselves accepting below market fees for their players as a result. We did that, so we feel we deserved more.