A late Charlie Austin goal condemned Arsenal to their first defeat in 23 games as Southampton snatched a thrilling 3-2 victory at St Mary's.
Danny Ings had twice given the Saints the lead before Arsenal fought back twice through Henrikh Mhkitaryan. But it was Austin who had the last laugh, coming off the bench to head home with five minutes to go.
Unai Emery was forced into putting together a makeshift back three, with Granit Xhaka filling in alongside Laurent Koscielny and Stephan Lichtsteiner.
But it was the Gunners who had the first opportunity to open the scoring. Pierre-Emerick Aubameyang broke in behind Maya Yoshida to recieve a long pass but the Gabonese striker was denied by a smart stop from Alex McCarthy.
The Arsenal backline soon showed signs of vulnerability when Nathan Redmond and Stuart Armstrong both having efforts saved by Bernd Leno.
And the home side found the opener shortly after, with Targett whipping a superb cross beyond Koscielny and Ings headed past Leno.
Mkhitaryan soon restored parity, arriving late in the box to head Nacho Monreal's floated cross into the corner.
Ings then struck again on 44 minutes, looping his header into the top corner to put Ralph Hasenhuttl's side back in front before the interval.
The Gunners, as they often do in the second half, rallied and found themselves level with some good fortune when Mkhitaryan's effort was diverted into the net by Jannik Vestergaard.
Both sides had opportunities to get the winner and it looked to be heading for a draw before Austin rose to meet Shane Long's floated cross. Leno couldn't reach it and the striker headed home into an empty net.
Arsenal are finally beaten and it will be interesting to see how they respond after losing for the first time since August.
