Frank Lampard’s men were once again indebted to the Spanish full back after Bournemouth overturned Chelsea’s first half lead with two early second half goals.
Chelsea remain in fourth place while Bournemouth are one place above the relegation zone.
Bournemouth had the opportunity to take the lead twice in the first five minutes through Philip Billing. The Denmark international’s low shot from Jack Stacey’s delivery was parried away by Willy Caballero in the 3rd minute before the former Huddersfield midfielder found the side netting when through on goal after robbing Fikayo Tomori in his own box a minute later.
Mason Mount then tested Aaron Ramsdale from range with a dipping volley in the ninth minute after Bournemouth could only half-clear a corner.
For the second time in a week Alonso scored to give Chelsea the lead when he lashed in inside the six-yard box after Olivier Giroud’s effort from Reece James’ cross struck the crossbar in the 33rd minute.
Bournemouth looked galvanised after the break, but it was Chelsea who should have doubled their tally when Giroud dragged his shot wide following good work from Mateo Kovacic in the 49th minute.
But the hosts got a deserved equaliser after 54 minutes when Jefferson Lerma powerfully headed in Ryan Fraser’s corner.
Chelsea fell behind just three minutes after conceding the equaliser as Josh King tapped home Stacey’s low cross at the far post unmarked.
Five minutes before full time, Alonso popped up once again in the Bournemouth penalty box to head home Chelsea’s equaliser after Ramsdale saved Pedro Rodriguez’s shot onto his path.
The Spanish full back could have sealed all three points for the visitors in stoppage time but he headed a good cross into the box wide of the far post.
