Danny Ward was Leicester’s hero at Wolves as the three-time winners squeezed into the Carabao Cup fourth round on penalties.
The goalkeeper saved spot kicks from Romain Saiss, Diogo Jota and Adama Traore as the Foxes won the shootout 3-1 following a 0-0 draw at Molineux.
But victory came at a price as the Foxes will be concerned after a bad injury to Demarai Gray.
The winger was carried off with his left leg in a brace and received oxygen on the pitch after an injury-time challenge with Ryan Bennett.
Leicester deserved their victory and Marc Albrighton was thwarted three times by John Ruddy while Ruben Vinagre went close for the hosts, who rarely threatened.
The Foxes were on top from the start and Vicente Iborra drilled wide after five minutes as Leicester bossed the early stages without forcing Ruddy into a save.
Wolves, who last won the League Cup in 1980, were disjointed with Traore quiet as Iborra dictated the play at Molineux.
But Leicester’s lack of punch, for all their hard work, would have frustrated boss Claude Puel and Wolves nearly punished them during a generally sedate first half.
Jonny Otto fired over from Ivan Cavaleiro’s knock-down after 20 minutes before Ward tipped over Vinagre’s driven effort.
That they were the only serious chances for the hosts, who made nine changes from the 1-1 draw at Manchester United, underlined how placid they had been having demonstrated verve and flair since returning to the top flight this season.
Leicester continued to be the more composed and nearly broke the deadlock when Conor Coady hacked away Rachid Ghezzal’s effort off the line nine minutes before the break.
Marc Albrighton stung Ruddy’s palms from 18 yards and, following the re-start, Ricardo Pereira drilled a half volley wide.
Wolves briefly improved but relied on Ruddy’s excellent reflexes after 67 minutes when he denied Albrighton from almost point blank range following Ghezzal’s teasing centre.
By then Leicester had already withdrawn Jamie Vardy, a surprise starter, and Shinji Okazaki in preparation for Saturday’s trip to Newcastle.
Morgan Gibbs-White shot straight at Ward but it was a rare bright moment for the hosts and they were fortunate when Albrighton miscued a free header from eight yards.
Bennett came closest to breaking the deadlock in injury time when he headed over before Gray was carried off following lengthy treatment after appearing to get his left ankle caught under him.
The game was then decided on penalties with Ghezzal, Iborra and Kelechi Iheanacho scoring for Leicester while Christian Fuchs and Hamza Choudhury missed.
Benny Ashley-Seal scored for Wolves but Ward denied Saiss and Jota before brilliantly turning Traore’s effort onto the post.
