Mauricio Pochettino was left disappointed by Tottenham's failure to build on a positive start as they lost 2-1 to Anderlecht despite taking an early lead.
Spurs surrendered top spot in Europa League Group J as Christian Eriksen's fourth-minute goal was eclipsed by efforts from Guillaume Gillet and Stefano Okaka in Belgium.
A disappointed Pochettino told ESPN: "We created in the first 10 minutes three chances, we score for 1-0.
"Then we lose the focus on the game after 13 minutes and it's very difficult to come back again.
"It looks or seems easy and this sometimes happens and for that we are very disappointed, not only the result but the performance because I think that we started the game very well, but we lost our focus on the game."
With Monaco having beaten Qarabag 1-0 on Thursday, just two points separate all four teams in the group after three games, with Spurs second.
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