Arsenal were left to rue several missed chances as they squandered the opportunity to go top of the Women's Super League.
The 1-0 defeat to bitter North London rivals Tottenham will add salt to the wounds.
Scottish striker Martha Thomas scored the only goal of the match just before the hour mark.
The goal ensured Spurs gained their first-ever victory over the Gunners in the WSL.
The game was played at the Tottenham Hotspur stadium with Tottenham owner Daniel Levy in attendance.
Spurs remain sixth after their first win in six league games.
Arsenal got the better of Spurs in a cracking 3-3 draw that was decided on penalties in the Conti Cup during the week.
Today, saw different lineups and a different energy to the game.
Had Arsenal been victorious they would have sat top of the pile ahead of Chelsea's trip to Bristol City on Sunday.
The Gunners came closest in the first half when Caitlin Foord struck the post in what was a hard-fought first half.
Arsenal continued to control the match after the break.
Alessia Russo sent a header off target from just six yards out and then Frida Maanum fizzed another effort inches over the bar from wide on the left.
Shock lead
But Spurs held steady and took a shock lead in the 58th minute.
A quick, passing move from the defence ended with Martha Thomas sliding in from Celin Bizet's low cross.
The ball found the corner and Spurs were ahead.
Arsenal pressed hard but to their credit the Tottenham defence held firm.
Barbora Votikova was named Player of the Match after an excellent debut as the Spurs' netminder.
After the game Votikova said
"It felt really good to beat them."
A clean sheet and a win on your debut against your club's fiercest rivals - not a bad Christmas present.
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