Spurs struggled to find their rhythm at Vicarage Road, as a stubborn Watford backline stood firm against an unusually flat Lilywhites side.
A stroke of good fortune got Tottenham their opener when a deflection off Abdoulaye Doucouré crept past Ben Foster, before the hosts fought back with goals from Troy Deeney and Craig Cathcart to swing the game in the Hornets favour.
It might be an overreaction, but I think we may have gone too soon with the conclusion about Tottenham's summer being for the best. Three wins from four - pretty good - but all of those games have had "moments".— Seb Stafford-Bloor (@SebSB) September 2, 2018
Pochettino was far from pleased with his side's efforts, telling Sky Sports that his team were simply not good enough: "First half we were so relaxed, so sloppy, We dominated the game but we weren’t aggressive enough.
"When you want to win and show you are a contender you cannot say we are going to play football for five minutes and in the second half we are going to win.
“In two set-pieces we concede two goals. If you want to be a contender, if you want to be on the top you cannot concede this type of action. You need more strength defending because in that situation it is when you really show that you want to win. It is not about the talk.
“It is the reality and everyone saw the reality. It is so easy to explain what happened on the pitch in 95 minutes. When you lose you must learn and improve but my disappointment is when you win and maybe you didn’t deserve to win, why no learn?
“During the week I was trying to explain to the players we weren’t as great as the perception and the reality was completely different.”
Spurs will hope to bounce back from Sunday's defeat after the international break when they face a rampant Liverpool side, who top the Premier League table after their fourth win in a row against Leicester.