Seven weeks ago, Steve Marks, a longtime aide to Democratic gubernatorial candidate John Kitzhaber, was worried about the strength and financial advantage Republican nominee Chris Dudley was displaying.

“I was nervous,” Marks said in a sweltering Hilton Hotel ballroom Tuesday evening at Kitzhaber’s election night party. Shouting above Bruce Springsteen, Marks added that such concerns were new for Kitzhaber, who won governor’s races handily in 1994 and 1998.

“We had to run a much more aggressive, active campaign this time,” Marks said. “Dudley did not have a record we could run against and he had a lot of money.”

As the night wore on, veteran campaign operatives expressed confidence that a late avalanche of votes in Multnomah County would make the difference in a race that remained deadlocked. In 2006, when Democratic incumbent Ted Kulongoski won re-election as Oregon governor by 110,000 votes, that margin reflected the difference in heavily Democratic Multnomah County.

Political strategist Mark Wiener, who worked on the Kitzhaber campaign, said he anticipated a similar pattern in 2010.

“I’m feeling cautiously optimistic,” Wiener said.

If Kitzhaber ends up winning, the difference may end up being a late voter-registration surge. Although the Secretary of State’s Elections Division has tallied a consistent Democratic registration advantage for the past few months, three groups quietly enlisted tens of thousands of new voters: the Bus Project signed up 20,000, according to the Bus’s Caitlin Baggott; the Oregon Student Association signed up 25,000; and Defend Oregon signed up another 25,000.

UPDATE: Just before 11 pm, Kitzhaber strode onstage looking uncharacteristically happy.

“We’ve known all along it would be close and it would come down to Multnomah County,” Kitzhaber told the crowd. “And almost half of Multnomah County’s votes aren’t in yet.”

Kitzhaber credited what he called the “best field operation in Oregon history. And he predicted that field operation would yield a result similar to U.S. Sen. Jeff Merkley’s come-from-behind victory as the Democratic challenger over Republican Gordon Smith in 2008.

“Jeff Merkley went to sleep in this position [a couple of percentage points behind],” Kitzhaber said. “And he woke up a U.S. senator.”