"The transition doesn't come as too much of a surprise to us as Mr Maestri left his position as Xerox's CFO to become Apple's corporate controller, which we felt was an indication that there must be an eventual path to CFO," Wells Fargo Securities analyst Maynard Um said in a research note.
"While we view Mr Oppenheimer's retirement as a loss to the company, we expect the transition to be fairly seamless."
Oppenheimer, who was named to the board of Goldman Sachs on Monday, said he would use some of his free time to complete his pilot's license.
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Cross Research analyst Shannon Cross said Oppenheimer's move had nothing to do with his new role at Goldman Sachs.
"There is nothing there. This was absolutely a 100 percent planned transition," Cross told Reuters.
Cook noted that Apple's revenue had risen to $171 billion from $8 billion during Oppenheimer's tenure as CFO.
Maestri will take over his new role at a time when Apple has been under pressure from investors such as Carl Icahn to return much of its huge cash pile to investors and to come up with the next big thing to emulate the success of iPhone and iPad.
The company had about $160 billion cash at the end of 2013.
Apple has said it will return $100 billion to shareholders by the end of 2015 through dividends and share repurchase.
The company said in February that it had bought more than $40 billion of its shares over the past 12 months, helping to satisfy Icahn, at least for now.
Apple shares were up 0.7 percent at $531.22 in early trade on the Nasdaq. (Click here for the latest quote.)