Vardy was left on the bench for the second successive Premier League fixture on Sunday
Vardy was left on the bench for the second successive Premier League fixture on Sunday as the champions were beaten 2-1 by West Brom.
Okazaki partnered Islam Slimani who scored Leicester's only goal after James Morrison had given West Brom the lead.
Vardy, last season's leading scorer, made little impact after stepping off the bench at half-time.
"In this moment we play better with Shinji Okazaki," said Ranieri.
"Today, we didn't, but often we do. I didn't play Islam Slimani in the Champions League and I wanted to give a rest to Vardy.
"But it wasn't right, they didn't do what I asked so in the second half I introduced Vardy to attack the defensive line."
Meanwhile, Ranieri backed Danny Drinkwater to bounce back from the howler that ended their 20-match unbeaten home Premier League record.
Drinkwater's dreadful backpass handed Matt Phillips the winner for West Brom to inflict Leicester's first home league defeat for more than a year.
Ranieri apologised to supporters for the end of the run but insisted England midfielder Drinkwater will respond positively.
"I am very sorry we lost our unbeaten record at home," said Ranieri, whose side maintained their unbeaten Champions League record on Wednesday with a goalless draw in Copenhagen.
"But we knew it would be a tough match against West Bromwich. It was the same last season in the 2-2 draw.
"The first half was not good. We tried to have a plan but it was difficult to do this. The second half was much better but we lost the match."
He added: "Danny has said nothing. Every player can make mistake. What can you say to him?
"He is one of our best players. It is no problem. He will overcome that, of course."
For West Brom, a third victory of the season came thanks to Phillips' first goal for the club.
The summer signing from QPR had been dropped last weekend but was recalled at Leicester for the suspended James McClean and laid on Morrison?s goal before scoring himself.
"The biggest problem with Matt is that self-belief," said coach Tony Pulis, who pursued Phillips for more than a year before signing him in the summer.
"He's got all the tools, he's very quick, he's got two great feet and he's got a good goalscoring record.
"I had a chat with him last week and told him he has to start understanding that he's a good player and he deserves to be where he is."
West Brom triumphed without Saido Berahino after the striker was sent to France for a four-day fitness camp, from where he posted a pre-match Instagram photograph showing off his muscles with the caption "fat boy".
Pulis joked: "He's looking nearly there. Nearly!"