Toronto, Canada – The 38-year-old Ukrainian spent the entire fight on the offensive against previously unbeaten Johnson but could not find his customary knockout as his opponent opted for survival.
A sell-out 17,000 crowd at Berne's PostFinance Arena willed the 38-year-old Klitschko to finish the job inside the distance, as he had done in 37 of his previous 38 victories from 40 fights, but Johnson's chin was up to the task, even though he rarely landed a meaningful punch.
"He was a very unusual fighter," Klitschko said at ringside after his fourth win since returning to action in 2008 following an injury-induced retirement in 2005.
"He moved very well and was not easy to hit. I'm disappointed because I would have preferred a knockout but I'm happy that I won all 12 rounds."
Johnson's chief tactic appeared to be to irritate the champion, gesticulating throughout the fight and pointing to his chin and tempers flared briefly at the end of the 11th when the fighters traded punches after the bell.
Vladimir Klitschko, Vitali's younger brother and holder of the WBO, IBO and IBF, also became involved in a brief exchange with Johnson after the final bell at the end of the 12th.
Klitschko said he hoped to take on Briton David Haye, who beat Russian giant Nikolai Valuev last month to win the WBA belt, in a unification fight next year.
"I'm ready," Klitschko said. "I will be happy to fight him next year. David Haye is the trash talking world champion."
(Reporting by Martyn Herman; Editing by Ian Ransom)