Zynga Inc's shares, which have been below $5 for over a year, were down as much as 11 percent at $2.58 in extended trading following the news.
Sterne, Agee & Leach analyst Arvind Bhatia said the leadership change had sent the "wrong message" because the San Francisco-based company was beginning to move in the right direction under Mattrick.
Mattrick, who Zynga said will receive a $4 million payout, was given the top job in 2013 to help turn around the company's waning fortunes after it failed to capitalise on the popularity of its "FarmVille" game with new hits. As chief executive, he focussed on accelerating Zynga's mobile game efforts.
Pincus stayed on as Zynga's chairman and chief product officer at the time and relinquished the last of his operational duties last year.
The company said he has requested an annual salary of $1 as CEO.
Mattrick, who headed Microsoft Corp's Xbox business before joining Zynga, will also leave the board, the company said.
"I plan to return to Canada to pursue my next challenge," Mattrick said in a statement.
Barclays analyst Chris Merwin said Zynga now needs "to prove they're able to execute even during yet another leadership transition if they hope to regain investor's confidence."
Zynga suffered a dramatic reversal of fortune in 2012 as gamers dropped its lucrative, Facebook-based desktop games for mobile offerings from rivals such as King Digital Entertainment Plc, maker of "Candy Crush Saga.
Pincus founded Zynga, once one of Silicon Valley's fastest growing companies, in 2007, and the path to recovery has been tortuous. It posted a loss of $226 million last year and non-GAAP revenue dwindled to $694 million from $1.15 billion in 2012.
In February, Zynga said it would launch six to 10 new mobile titles this year after it reported bookings of $182.4 million, about $19 million less than expected, according to research firm StreetAccount.
The company is also facing a U.S. lawsuit that accuses it of defrauding shareholders about its prospects before and after its December 2011 initial public offering.
© Thomson Reuters 2015