West Ham United were leapfrogged by Arsenal in the Premier League table following a 2-0 defeat at the home of their North London rivals.
Clinical finishes at the start and end of a fiercely-contested second half ultimately proved the Hammers' undoing in a match they finished with ten men, following a contentious second yellow card for Vladimír Coufal midway through the period.
Gabriel Martinelli had raced clear to roll the ball past Lukasz Fabianski two minutes after half-time, the Pole later superbly saving Alexandre Lacazette's penalty kick having earlier turned Kieran Tierney's volley onto the crossbar.
The dismissal made West Ham's task all the more difficult in the closing stages as they sought a route back into the match, and Emile Smith Rowe eventually netted the home side's second goal on the counter attack late on.