With all precincts reporting, former elections chief .
Slocum claimed nearly 40 percent of the vote and Masur about 21 percent.
The two will be in a run-off election on Nov. 6.
"I am so humbled by the results," Slocum said at a party Tuesday night. "Especially having joined this race so late."
"Because this is a district-wide race, you have to know the issues from Redwood City to the coastside to Daly City," he said.
Slocum said he'll resume campaigning in a "quiet way" for the November run-off. "But tomorrow, I'll be back at it."
Masur said she is ready to continue her campaign.
“It’s been a joy to run in this campaign,” Masur said. “It’s made me remember how beautiful this county is and how lucky we are to live here.”
“Moving onto November, it’s going to be a lot of work,” Masur said of the run-off. “But I have every confidence that we can do it.”
“I’m so happy and gratified and feel fortunate that people put their faith in me."
And although he came in last place, Redwood City Planning Commissioner Ernie Schmidt said he still felt victorious.
"I'm still a winner because I took a step to run for public office," Schmidt said. "When you have a passion for your county and city, you want to work for it."
Schmidt made the decision to run because grew up in a family of public office holders, he said. Schmidt's great grandfather was the Governor of Mexico and his grandfathers were the counsel generals of Mexico.
"No matter what happens, this experience has made me a better leader as the Vice Chair of [Redwood City's] Planning Commission," Schmidt said.
District 1 Supervisor Dave Pine won his race unopposed, with 65,559 votes.
And District 5 Supervisor Adrienne Tissier also retained her seat, running unopposed, garnering 59,905 votes.
Here is the final Election Night report.:Board Member: San Mateo County Board of Supervisors, District 4 Vote by Mail Early Voting Election Day Total Votes Warren Slocum (39.04%) 20,885 193 8,219 29,2597 Shelly Masur (21.14%) 11,393 90 4,380 15,863 Kirsten Keith (14.93%) 7,798 70 3,338 11,206 Carlos Romero (8.78%) 4,567 43 1,978 6,588 Memo Morantes (7.92%) 4,079 44 1,818 5,941 Andy Cohen (5.03%) 2,512 27 1,234 3,773 Ernesto "Ernie" Schmidt (3.17%) 1,610 15 757 2,382