Spurs failed to hold on to the lead handed to them by Abdoulaye Doucoure's 53rd-minute own-goal at Vicarage Road, as Troy Deeney and Craig Cathcart scored via set-pieces to maintain the Hornets' ideal start to the season.
Watford host Manchester United in the league on September 15 after the worldwide break.
Romelu Lukaku got the two goals for the Red Devils, but there was a sour point as substitute Marcus Rashford was sent off in the 71st minute for pushing his forehead into Phil Bardsley's head.
While Stephen Ball admitted Watford were the better side on the day, Steve Bayford feels football fans are a fickle lot. Nevertheless, manager Mauricio Pochettino was wary that his side faced another tough challenge: "We're going to play on Sunday against a very good team - a team that's going to fight and is in a very good moment", he explained.
The Denmark playmaker said: "We're very disappointed".
"The reality is if you want to be a contender today we should win and win easy because everything was ready to win the game".
Despite not getting the win, Moura showed once more that his pace is going to be a trouble for defenders.
"We weren't at our best but when you go ahead you want to see out the game and we're disappointed not to do that".
"We conceded two goals that if you want to be a contender you can not concede".
"The reality is we need to analyse who is in the pitch". Pochettino was unhappy with that win and said Tottenham were lucky, but the away fixture to unbeaten Watford was another huge test and winning would've shown Spurs to be potential title challengers. "But the last three wins, when we won games, nobody asked me [about that]". In four games this season he's already scored three and caused the own goal against Watford, so there are no signs of his goal contributions stopping any time soon.