Bournemouth deepened Arsenal's misery with a 2-1 comeback victory on an afternoon when Alexis Sanchez's January exit appeared ever closer.
Hector Bellerin's scruffy finish to a fine move (52) looked like sealing a morale-boosting win for a side without the omitted contract rebel, but the hosts completed a second-half turnaround through Callum Wilson (70) and Jordon Ibe (74) to boost their survival hopes and further dent Arsenal's top-four ambitions.
Arsene Wenger had admitted before the game that Sanchez's future would be resolved imminently, but while an end appears in sight to the saga that has long cast a shadow, the on-field troubles continue for a Gunners team embarrassed in the FA Cup a week ago and now winless in five games in all competitions.
Bournemouth: Begovic (6), Francis (6), S Cook (6), Ake (6), A Smith (7), L Cook (7), Gosling (6), Daniels (5), Ibe (7), Fraser (7), C Wilson (8).
Subs used: Mousset (6), Pugh (6), Afobe (N/A).
Arsenal: Cech (6), Chambers (5), Mustafi (5), Holding (5), Bellerin (7), Xhaka (6), Wilshere (7), Maitland-Niles (7), Iwobi (6), Welbeck (5), Lacazette (5).
Subs Used: Ramsey (5), Walcott (5).
Man of the match: Callum Wilson
Wenger - without injured Mesut Ozil as well as Sanchez, and forced to watch on again from the stands - saw Bournemouth start the brisker, Adam Smith fizzing an early shot just wide of Petr Cech's post.
Ainsley Maitland-Niles twisted twice in the box to craft space, only to see his curling effort clip the bar (7), but though Jack Wilshere was impressing on familiar turf, real rhythm eluded both sides in a scrappy first half-hour.
Danny Welbeck was thwarted by the out-rushing Asmir Begovic as Arsenal upped the ante, but the hosts appealed justifiably for a penalty when Alex Iwobi repelled a corner with a raised elbow (39) and then were denied by gutsy defending, Calum Chambers sliding in to deny Ryan Fraser.
Alexis Sanchez was omitted from the Arsenal squad and Mesut Ozil was also not involved but Jack Wilshere shrugged off an ankle injury to play against his former loan club.
Lewis Cook and Dan Gosling started for Bournemouth with Harry Arter on the bench.
Bournemouth resumed with intent as the January sun broke through, but Arsenal made the breakthrough just seven minutes after the restart when Iwobi set free Bellerin with a slide-rule pass, his shot bobbling over the line after Begovic's half-save.
Eddie Howe threw on Lys Mousset, Fraser shuffled to right wing-back, but a momentum shift had not looked likely until Wilson struck, stretching out a boot and beating Cech and Chambers to a ball swung in invitingly by Fraser.
Wilson swiftly turned provider as Arsenal lapsed at the back again, the striker afforded time to control Smith's pass, before letting Ibe lash low.
Theo Walcott followed Aaron Ramsey off the bench but, having surrendered the lead, Arsenal never looked like mustering the response that earned Howe's men - now up to 13th - a timely first win over desperately disappointing opponents.
- Bournemouth have recorded their first win against a side from the 'big six' in the Premier League since December 2016 (4-3 v Liverpool), ending a run of 14 winless games (D3 L11), including nine successive losses.
- Arsenal have picked up just 13 points after 12 Premier League away games (W3 D4 L5) - their worst record at this stage of a season since 2005-06 (12 points from 12 games).
- Arsenal have lost the last three Premier League games that Alexis Sanchez hasn't played any part in - 0-1 at Stoke, 1-2 at Watford and today against Bournemouth.
- At average age of 25 years and 56 days old, Arsene Wenger named his youngest Arsenal starting line-up in the Premier League since November 2012 v Aston Villa (25y 11d).
Man of the match - Callum Wilson
Jordon Ibe struck the winner but Callum Wilson proved pivotal, showing desire to poach the equaliser and then strength to hold up a ball with back to goal and set up the decisive strike. He has now scored three goals in three Premier League games against the Gunners - and recorded his first Premier League assist in this contest.
Arsenal return to Premier League action next Saturday against a resurgent Crystal Palace side - their Carabao Cup semi-final decider against Chelsea four days later - while Bournemouth travel to West Ham.