Arsenal missed the chance to go top of the Premier League as West Brom came from behind to win 2-1 at the Hawthorns on Saturday.
Olivier Giroud headed home Mesut Ozil's free kick to put the Gunners in front, but a James Morrison volley and a Mikel Arteta own goal turned things around in a five-minute spell before the break.
Ozil hit the post in the second half but Arsenal - who lost Francis Coquelin and Arteta to knee and calf injuries respectively - couldn't find their way back into the game as Santi Cazorla missed a penalty late on.
The result means Arsene Wenger's have not yet won in November in all competitions, as they turn their attention to the Champions League clash with Dinamo Zagreb in midweek.
Arsenal knew at least a draw would send them top of the league - for a few hours at least - and they started well, keeping possession despite not creating too many opportunities until Alexis Sanchez went close with a curling free kick from 25 yards, which was saved by Boaz Myhill.
West Brom had a couple of chances from set pieces of their own, but the hosts struggled with poor deliveries, and eventually fell behind to an Arsenal free-kick in the 28th minute.
Sanchez was brought down on the right and Ozil whipped it into the box, where Giroud was left unmarked to flick a header beyond Myhill and into the far corner.
Arsenal's lead would only last seven minutes, though, as the Baggies won another free-kick and captain Chris Brunt's superb delivery was met by an equally brilliant volley from Morrison, who fired the ball straight into the top corner.
Things went from bad to worse for the visitors as West Brom caught Ozil in possession before Rondon collected it in the Arsenal half. The striker found James McClean on the overlap, and the winger's cross was diverted into his own net by Arteta (40).
Arsenal looked to find a way back quickly after the break and Ozil went close as the ball dropped for him 18 yards out, only for his low effort across goal to come back out off the upright.
Wenger threw on Joel Campbell as he looked to inject some life into his side just after the hour mark, but only a few minutes after coming on the Costa Rica international spurned a glorious opportunity.
Cazorla clipped a delightful ball over the top which dropped for Campbell just a few yards out, but he could only slice well wide with the goal at his mercy.
West Brom then nearly made him pay for the miss as Jonas Olsson powered Brunt's corner against the crossbar, but all the pressure was at the other end as Arsenal looked for an equaliser.
The Gunners' best chance came as Brunt was penalised for bundling over Sanchez in the box, but Cazorla slipped as he took the resulting spot-kick and ended up firing it way over the bar.
It would prove costly for the visitors as they couldn't fashion another chance and West Brom held on to take victory.
Matt Le Tissier's Soccer Saturday verdict
"It makes me think that perhaps the one thing that might stop Arsenal winning the title is their strength and depth. With the injuries that they've got, you look at what they put out there, you look at the bench to try and change the game and it wasn't a great deal. They brought Joel Campbell on for Kieran Gibbs and that was the only option they had in terms of attacking players. You looked at the rest of the bench and you didn't see there being any game-changers."
West Brom: Myhill (7), Dawson (6), Evans (8), Olsson (6), Brunt (7), Morrison (7), Fletcher (6), Yacob (6), McClean (7), Sessegnon (5), Rondon (6).
Subs used: Gardner (6), Lambert (6), Berahino (6).
Arsenal: Cech (6), Bellerin (6), Koscielny (6), Mertesacker (5), Monreal (6), Coquelin (6), Cazorla (4), Sanchez (8), Ozil (7), Gibbs (5), Giroud (6).
Subs used: Arteta (3), Flamini (5),Campbell (4).
Man of the match: Jonny Evans