Frank Lampard ordered Chelsea to cut out the mistakes as his side scored a 93rd-minute equaliser to complete an astonishing comeback after trailing West Brom 3-0 at The Hawthorns.
The Baggies looked to be racing to a first win since returning to the Premier League after errors allowed Callum Robinson, twice, and Kyle Bartley to score before half-time.
But goals by homegrown players Mason Mount, Callum Hudson-Odoi and Tammy Abraham - the third deep into stoppage time - rescued a point for the big-spending Blues.
It was a dramatic end to an incident-packed game and Chelsea boss Frank Lampard, who has spent £200m-plus strengthening his squad this summer, said he had mixed emotions after the match.