Arsenal were in absolute control of their trip to Watford at half-time, commanding a 1-0 lead virtue of Per Mertesacker against a poor Hornets side.
Whatever Marco Silva said to his team during the break, though, worked absolute magic against Arsene Wenger's men.
Troy Deeney levelled the scores from the penalty spot after the referee punished Hector Bellerin for a controversial challenge. Then, deep into stoppage, Tom Cleverly scored his first Watford goal in seven years to inflict that same sinking feeling upon Arsenal fans.
Questionable refereeing decisions certainly played their part but there can be no doubting that Arsenal dissolved in the second-half, a process accelerated by the departure of Danny Welbeck.
Nevertheless, a great deal of credit is due to Watford who sit above the likes of Liverpool, Chelsea and Arsenal themselves in the Premier League table after eight games.
Marco Silva gained no shortage of admirers after a spirited job at Hull City last season and was seen as a brilliant coup by Watford this summer.
Impressive away victories against Bournemouth and Southampton as well as dramatic stoppage time goals versus Swansea City and West Brom see Watford absolutely flying.
One man who wasn't convinced at the start of the season, though, proves a certain Paul Merson.
The ex-England international has something of a reputation for utterly bizarre predictions and it seems his old team - Arsenal - have dug him yet another hole by making a mockery of his August forecast.
There was doubt cast over Watford ahead of the new season after the Hornets completely self-destructed under Walter Mazzarri during the final months of the campaign.
When asked whether Watford would thrive under Silva, Merson dropped this scandalously assured prediction: "No, they will get relegated."
Well then, it's settled.
Although Watford's form suggests the exact opposite, let's allow the Merson of two months ago to explain his conviction.
He continued: "To have a manager who has enhanced their reputation by being relegated is remarkable. He had the chance to bring in players and didn't achieve what he was brought in for.
"Will Hughes looked a decent player and he was doing well in the Championship but it is a different challenge entirely stepping up to the Premier League."
It got worse, however: "I worry about them. They struggled last season and have no momentum so I'm going to place them 18th."
We're only in October and Merson might just have dropped his biggest clanger yet - Watford are absolutely flying.
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