Andre Villas-Boas' side have won six of their last eight league games and sit three points ahead of local rivals Arsenal in a top four race which looks set to go right down to the wire, with Everton and West Brom in close pursuit.
The busy festive period always offers up a congested fixture list and Dembele has argued that despite Brian McDermott's side struggling at the bottom end of the table for most of the campaign, their upcoming clash at White Hart Lane is far from a foregone conclusion.
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"Everyone expects that we’ll go out there and win but it won’t be easy. We have to be 100 per cent concentrated for this game."
Spurs' 2-1 victory at the Stadium of Light on Saturday saw them into fourth place in the Premier League after coming back from a goal behind, and Dembele feels that this sort of battling form will stand them in good stead going forward.
"Everyone knows Sunderland is a difficult place to play, so we’re very happy with the win," he added.
"We played very well and went 1-0 down, but we all believed if we played the same way in the second half then we’d get a good result.
"We had a great mentality, everyone trying to motivate each other and it worked.
"We’re playing well as a team, playing good football and things are going well for me as well personally. That makes it much easier to play my game. Yes, I’m very happy at the moment."