In the end, Michael Nutter finished with 106,805 votes, 36.6 percent, to Knox's 71,731 votes, 24.6 percent.
Since then, though, Knox has been just another flirt.
In 2010, he hired consultants and started running for governor, threatening to spend $15 million, before withdrawing.
A year later he said he'd jump into the Democratic primary to stop Mayor Nutter's reelection, vowing to match the incumbent dollar for dollar. Never happened.
Last December, Knox passed out business cards advertising his campaign for governor in Manhattan during the gilded pub crawl/lobbyfest known as the Pennsylvania Society. Former Gov. Ed Rendell was touting him as gubernatorial timber for months to anyone in the state political world who would listen. Lately he is said to have been encouraging Knox to run for mayor.
Six years ago, Knox's strength was his ability to spend beyond the limits of city campaign-finance law. In the post-Citizens United environment, that may not matter much. Many expect that, in 2015, outside groups will spend outside the limits to back favored candidates.
State Sen. Tony Williams, for instance, financed his 2010 campaign for governor with millions of dollars from a group of investors who share his commitment to charter schools. Williams is looking at the 2015 mayoral race.
Knox's tale brings up another point - although party power brokers are always encouraging "self-funders" to run for office because it makes their jobs easier and frees resources for other races, the record of rich candidates who foot most of their own bills is abysmal.
Only nine of the 49 candidates for Congress who spent significant sums of their own cash to run for the U.S. House and Senate in 2012 won, according to the nonpartisan Center for Responsive Politics.
Among the losers: former wrestling impresario Linda McMahon, who spent $43 million to lose her second Senate race in Connecticut.
There have been successful rich candidates with great resumés, including New York Mayor Michael Bloomberg, who spent $250 million of his fortune on three races. Far more common, say political scientists, is the case of Meg Whitman, the former chief executive of eBay and current head of Hewlett-Packard, who spent $142 million in her 2010 losing bid for California governor.
Jennifer Steen, a political scientist at Arizona State University who wrote a book on the subject, concludes that candidates who raise money from thousands of donors show strength and help build a base of support. In addition, she says, most self-funders lack the experience in politics that builds a campaigner's skill.
Knox, who made his millions in insurance and other businesses, was a deputy mayor of Philadelphia under Rendell for 19 months in 1992 and 1993. He has held no office and has no natural base of popular support.
Still, he told The Inquirer last week, he was serious about 2015.
"What does that Ivory soap commercial say - 99.44 percent?" Knox said.
Contact Thomas Fitzgerald at 215-854-2718 or firstname.lastname@example.org, or follow @tomfitzgerald on Twitter. Read his blog, "The Big Tent," at www.philly.com./BigTent.