Arsenal scored twice in the last nine minutes to overcome in-form Watford and record their seventh straight win in all competitions.
With 10 minutes to go it appeared that the fourth-placed Hornets, who have beaten Tottenham this season, would frustrate another Premier League giant.
But that was until the introduction of Alex Iwobi midway through the second half at Emirates Stadium.
The Nigerian’s driven low ball from the right resulted in Arsenal’s opener, inadvertently turned in by Watford’s Craig Cathcart.
Two minutes later Iwobi was involved in a one-two with Alexandre Lacazette, who delivered a low cross for Mesut Ozil to sidefoot home.
With the game goalless, Arsenal substitute keeper Bernd Leno made a great one-handed save to deny Troy Deeney, while Issac Success fired narrowly wide of the far post.
They have won five games in a row in the league to climb to fifth in the table, while Ozil has rediscovered his scoring touch with three goals in four matches in all competitions.
Emery, who replaced long-time servant Arsene Wenger in the summer, made two key tactical decisions against Watford, bringing on Iwobi for Aaron Ramsey and sticking by Lacazette in attack.
Ramsey, who looks to be heading for the exit, shook his head as he was replaced by Iwobi in the 63rd minute. The Wales player failed to influence the game, while Iwobi added pace to midfield to complement the speed of Arsenal’s front two on the break.
It was from two swift attacks that Arsenal broke the deadlock. Iwobi first sped down the left before delivering a cross that the unfortunate Cathcart converted under pressure from Lacazette.
Arsenal caught out Watford again moments later, Ozil capping a move that was typical of those created during the pomp of Wenger’s reign.
Before the goals, Lacazette was the biggest threat on the pitch, but he wasted two good chances – a one-on-one with keeper Ben Foster and a header over the bar from eight yards.
However, Emery stuck by Lacazette – a £46.5m signing in 2017 – and he played a big part in the two goals.