The full-back had given the visitor, reeling from a 3-0 midweek loss to Bayern Munich in the Champions League, a first-half lead at the Vitality Stadium.

But quickfire second-half goals from Jefferson Lerma and Joshua King looked set to pile the misery on Blues boss Frank Lampard.

However, Alonso had the final say, heading home five minutes from time after Aaron Ramsdale could only parry Pedro's strike.

Philip Billing had two excellent chances inside the opening five minutes as Bournemouth made a promising start.

Willy Caballero produced an instinctive save to repel a first-time effort from the Dane, who then nicked the ball away from a sleeping Fikayo Tomori before drilling hurriedly into the side netting. 

It was not all one-way traffic, though, and Mateo Kovacic's dipping shot called Ramsdale into action, before Callum Wilson's strike brought another stop from Caballero. 

Alonso broke the deadlock in the 33rd minute when he fired into an empty net after Olivier Giroud had flicked Reece James' cross onto the crossbar, with Ramsdale having already committed to the first attempt.

Giroud fluffed his lines badly from eight yards out early in the second half and was made to pay as the hosts struck twice in three minutes.

Lerma's header from Ryan Fraser's delivery was too hot for Caballero to handle and the turnaround was complete when King tapped home from Jack Stacey's cross.

A hail storm arrived in the final 25 minutes and Lampard had a face like thunder when substitute Michy Batshuayi had a goal ruled out for offside, only for Alonso's late intervention to ease his worries.