Chelsea were 3-0 down at half-time of their clash with West Brom on Saturday.
Callum Robinson's brace and a Kyle Bartley strike stunned Frank Lampard.
Thiago Silva made an error on his league debut as Willy Caballero struggled.
Fans were enraged on Twitter, with some calling for Lampard to be sacked.
Chelsea's summer spending was supposed to close the gap to Liverpool and Manchester City this season, instead fans are raging at a shocking first-half.
The Blues found themselves 3-0 down to West Brom at half-time on Saturday night, with Callum Robinson scoring in the fourth and 25th minutes, before Kyle Bartley left Chelsea with a mountain to climb just two minutes later
New signing and Premier League debutant Thiago Silva's slip was at fault for Robinson's second, with Frank Lampard's men reacting sluggishly.
Willy Caballero, brought in for the dropped Kepa Arrizabalaga, was no improvement on the out-of-form Spaniard either.
Lampard's spending has totalled more than £220m this summer, bringing in seven new faces including Kai Havertz and Timo Werner.
While Ben Chilwell, Hakim Ziyech, Edouard Mendy and Malang Sarr are yet to feature for the club and others are bedding in, the collapse is a severely worrying sign for the Blues.
Many fans are already losing patience, with @Kovaholic writing: 'Sack him in the tunnel. I've not witnessed anything more embarrassing in 15 years of watching Chelsea.'
Echoing the criticism of Lampard, @ekwunife_dan added: 'Sign all the players in the world, it will never cover Lampard's useless tactics.
'Lampard has been exposed! He is just another average English manager. No style. No tactics.'
Chelsea finished fourth last season and are looking to build towards a title challenge but Frank Lampard clearly has serious work to do on his defensive organisation.