Pierce will now receive a daunting assignment: end Republicans' 34-year shutout from Oregon's top office.
Pierce secured 47 percent of votes, while Alley received 30 percent, according to partial returns.
Pierce, who has never run for office, announced months before the election and spent hundreds of thousands of dollars of his own money. Alley, a Lake Oswego investor who failed to win his party's nomination in 2010, entered the race just before the filing deadline after months of rumors.