The arrival of seven summer signings had led to a swell of optimism among the Tottenham support, but the bubble burst on Sunday afternoon when West Ham crushed their London rivals 3-0 at White Hart Lane.
On paper, the contest looked a mis-match. Spurs had almost £100million worth of new talent at their disposal while the only two new signings West Ham could call on were free transfer Razvan Rat and £5million man Stewart Downing.
Spurs threw away points at home against West Brom, Norwich, Wigan, Stoke and Fulham last season, but they had no trouble beating weaker opposition this term until Sunday.
Dembele believes any more slip-ups like the one against the Hammers could prove costly.
"If we want to be there with the top four we need to win these games," the Spurs midfielder said.
"You see the top teams, if they want to be champions, they have to win these small games and you can see it's the difference with the guys who become champions, they win these small games."
With so many talented new players in their team, Spurs will have to psychologically adjust to the fact that they will be favourites in most of the games this season, Dembele feels.
"It's easier to play against the top teams for the motivation but if we want to be a top team we need to be concentrated for these kind of games," the Belgian said.
"It's a mental thing. We have to talk with the team and we need to concentrate each other. It's normal. We have a lot of players and you can change very quickly the team, so everyone needs to know it's a difficult season."
Source: PA
Source: PA