Board Thread:Versus Debates/@comment-31568508-20170327125927/@comment-26369387-20170402001117

@Lorenzo.r.1st Not quite: Kakashi perfected Chidori after he got Sharingan. Before that, he used it first time in combat during Third Shinobi World War, but due to tunnel effect caused by great speed, Kakashi couldn't react to counter of Iwa shinobi and almost got killed, hadn't Minato saved him. After getting Sharingan from Obito shortly afterwards, with it's abilities Kakashi could use Chidori safely and eventually upgraded it to Raikiri.

It's said right in the Chidori-article.