The champions are just two points above the relegation zone after their fifth loss of the season, a 2-1 defeat to the Baggies, on Sunday.
Matt Phillips' second-half winner, after Danny Drinkwater's mistake, saw the Baggies deservedly become the first visiting team to win at the King Power Stadium in the Premier League since September 2015
Islam Slimani had cancelled out James Morrison's opener but Leicester were poor again after Wednesday's Champions League 0-0 draw in Copenhagen.
They lost just three times in last season's shock title-winning campaign and Ranieri admitted their supporters deserved better.
He said: " I am very sorry we lost our unbeaten record at home
We knew it would be a tough match against West Brom
"The first half was not good
We try to have a plan but it was difficult to do this, the second half was much better but we lost the match
"We made a plan to go on the flank and make crosses from the flank
But we made very few and also we made some long balls and for the central defenders it was too easy
To say something is easy, to do it is more difficult
Maybe we had Champions League fatigue, I don't know.
"The atmosphere was good but of course if you play well the crowd support more
We have to work the crowd
The first half was difficult to enjoy for our fans, the second was much better
I can say only thank you every time to our fans."
Phillips' winner came after Drinkwater misplaced a back-pass and gave him a clear run on goal to outstrip Wes Morgan and beat Ron-Robert Zieler, but Ranieri refused to blame the England midfielder
He added: "Danny has said nothing
Every player can make a mistake, what can you say to him?
"He is one of our best players
No problem, he overcomes that, of course."
It was Phillips' first goal for Albion after a £5million move from QPR in the summer and Baggies boss Pulis admitted a pep talk last week had the desired effect
"The biggest problem with Matt is that self-belief," he said
"
He's got all the tools, he's very quick, he's got two great feet
He's got a good goalscoring record
Matty's biggest problem is - you can speak to him - it's that self-belief at times.
"That's all we can do, is give him that confidence
But we had a chat with him last week
He has to start understanding that he's a good player and he deserves to be where he is."
Victory ended the Baggies' five-game winless run and moved them above Leicester in the Premier League - three points clear of the relegation zone heading into the international break.
Pulis added: "We've got a long season ahead of us and nobody knows that more than me
We need to bring some quality in and have the commitment we've had today
"But it will be tough, everybody's fighting, whether it's at the top or the bottom
It's going to be a tough league this year.
"Obviously the result is fantastic
We played four top teams and we got four points, a point a game
When you think it's Tottenham, Liverpool, Man City and now at the champions."
Source : PA
Source: PA