Brown, the city's first black mayor, was unable to win outright re-election to a third, two-year term in Tuesday's six-way race. The major reason was City Councilman Orlando Sanchez who drew within a few percentage points of Brown in final, unofficial returns.
With 100 percent of the vote counted early Wednesday, Brown had 43 percent of the vote and Sanchez 41 percent. Another city councilman, Chris Bell, received 16 percent, and three other candidates shared less than 1 percent of the vote.
The Dec. 1 runoff will pit a black against a Hispanic for the first time in a Houston mayoral race and a spirited contest is expected from the candidates who differ widely on the issues.
Houston municipal elections are non-partisan, but Brown is a Democrat and Sanchez is a Republican. Brown commands strong support among Houston black voters, but Sanchez has built his own coalition among a growing number of Hispanic voters and Republicans.
"Tonight Houstonians voted for a change," Sanchez told supporters. "A majority of Houstonians went to the polls today and decided it was time for a change in Houston, Texas."
Sanchez has attacked Brown's record after two terms in office, accusing him of failing to budget properly for city projects, such as streets and the fire department. Brown has cited accomplishments, including less crime, low unemployment and new growth.
Since Sept. 11, Brown has also cited his previous experience in public safety as police chief in Atlanta, Houston, and New York, and service in the Clinton administration as the national drug czar. He was first elected Houston mayor in 1997.
Brown sounded confident of victory in a speech to supporters Tuesday night.
"We're going in now for the knockout punch" he said at the Aerial Theatre. "One down and one to go."
On another issue, Houston voters approved a ban on medical or other benefits for same-sex domestic partners of city workers, a controversial item that raised gay rights issues. Fifty-two percent of the voters approved the ban that was put on the ballot after a petition drive.
Dave Wilson, a conservative activist, gathered more than 20,000 signatures to force the referendum. His action came after Brown, a gay-rights supporter, proposed benefits for same-sex partners of city employees.
Houston has a history of wrestling with gay rights election issues. In 1984, the City Council banned discrimination against gay city workers, but the voters rejected it a year later in a referendum. In 1998, Brown issued an executive order to carry out the council's intent and it was challenged in court, but eventually survived the legal attack.