Liverpool manager Jurgen Klopp felt a slack second-half showing from his side meant West Brom deserved their 1-1 draw at Anfield.
The Reds looked set to go five points clear at the summit thanks to Sadio Mane's sublime 12th-minute strike.
Liverpool were dominant before the interval but gradually let their control of the contest slip, appearing less secure when Joel Matip limped off to add to Klopp's injury problems at centre-back.
Alisson saved from Karlan Grant but the hosts did not heed that warning as Semi Ajayi headed home via the post eight minutes from time.
"It was our own fault. I don't think anyone can expect that a team plays like West Brom in the first half, like a 6-4 [formation] or whatever it was," Klopp told Sky Sports when reflecting upon Albion's ultra-defensive approach before the break.
"I thought we did okay. We scored the goal and didn’t give anything away, especially no set pieces.
"Second half we didn't do the same again. Already in the first five minutes of the second half they had like three counter attacks. We gave them easy, simple corners.
"It was the only thing that they wanted to have and we gave it away. That's why it's our fault and that's why it is only one point instead of three."
While acknowledging the mental challenges of playing against a team comfortable within their defensive shell, Klopp did not think his players stuck to their task in the manner Sam Allardyce's side managed to – West Brom's boss has now gone unbeaten in his last four Premier League matches at Anfield, doing so with four different teams.
"It is an incredible challenge to stay active and lively when you constantly face 10 men," said Klopp, whose team dropped points from a winning position at Anfield against a side starting the day in the relegation zone for the first time since December 2016.
"To be fair, West Brom did their job exactly for 90 minutes. West Brom deserved the point because we didn't finish the game, we didn’t have enough clear-cut chances
"It is difficult to create. It's a busy period, all that stuff, it's all an explanation. In the end, everyone knows and feels we should have and could have done better.
"In the second half we played around, crossed the ball and instead of moving we didn't switch. It is not a game we will talk about in 20 years but it is a game we had to play and we didn't play as we could."
Liverpool are next in action at Newcastle United on Wednesday and might have to do without a specialist fit senior centre-back after Klopp confirmed an adductor problem for Matip
"He felt his adductor and we don't know more," said the manager, who is without long-term absentees Virgil van Dijk and Joe Gomez.