Even Jiraya aknowledges that Orochimaru is as strong as him throught the series.
You are so wrong,Kisame asks why to Itachi saying that he could...Which Itachi responds with "i already used Tsukyomi twice and i was forced to use amaterasu,i need to rest somewhere.."..
Itachi could have defeated Jiraiya alone if he intended too since he mandhandled Orochimaru so quickly and easily. He just didn't wanted to kill,much less one of Konoha greats..
Once again,go read the manga and watch the anime,Pein itself says that Jiraiya most certainly would have beat him if Jiraiya knew about the secret ahead of time...