Chelsea boss Frank Lampard admits his side must cut out the mistakes despite hitting back from 3-0 down to claim a late Premier League point at West Brom.
Tammy Abraham's injury-time leveller snatched a 3-3 draw to rescue the Blues from an embarrassing defeat.
The late equaliser survived a VAR review after the ball hit Kai Havertz's arm to add to earlier goals from Mason Mount and Callum Hudson-Odoi.
Chelsea gifted Albion a 3-0 lead after errors from Marcos Alonso and Thiago Silva allowed Callum Robinson to claim a brace and Kyle Bartley was left unmarked to add a third.
Lampard said: "I've got mixed emotions, I'm happy to see us fight to the last minute but I have to go back to the beginning and we conceded three goals from three shots on target.
"It was mistakes, clear mistakes that cost us. You can have as many meetings as you want but with those mistakes, you give yourself a mountain to climb. We lacked a bit if urgency in the team.
"We were punished. We showed great character but at the same time it's not a position you want to be in. They had three shots on target and we conceded three goals.
"Thiago Silva is going to be fantastic for us. I'm sure he'll stand up and say he made a mistake.
"If you make mistakes you'll have an opportunity to put them right, if you don't then your opportunities will be less and less. There's a lot of work to be done."
Lampard dropped Kepa Arrizabalaga for Willy Caballero with new goalkeeper Edouard Mendy not ready after his move from Rennes.
But the Blues' fragile defence imploded after just four minutes when Alonso lost possession to Matheus Pereira and he teed up Robinson to fire in.
The striker then made it 2-0 after 25 minutes when Thiago Silva let the ball run under his foot and Robinson raced through to score.
It was 3-0 three minutes later when Bartley volleyed in from close range when he was left unmarked.
Mount started Chelsea's comeback 10 minutes after the break, firing in from 25 yards and Hudson-Odoi pulled another back when he swapped passes with Havertz to beat Sam Johnstone.
Abraham then broke Albion's hearts when he tapped in stoppage-time after Johnstone parried Mount's effort – although West Brom boss Slaven Bilic was unhappy the goal stood because of a Havertz handball.
He said: "It's not maybe handball – it is handball. It's so obvious I don't even want to talk about it.
"The only mistake we made was the second goal, there was a foul (on Darnell Furlong) but the referee didn't give it. The third goal is hard to accept.
"We played the game we wanted to play. You can't plan you are going to outclass them but you can outrun them, have the right determination and concentration, make them make mistakes and punish them.
"We knew the second half was going to be hard for us. We knew we would have to defend as a team quite deep and the plan was to limit them to shots outside the box.
"It's disappointing as the boys did well enough to get all three points."
