Two candidates—Martin J. Walsh and John R. Connolly ’95—emerged Tuesday night as the first- and second-place winners, respectively, of a hotly contested preliminary round of voting for the Boston mayoral race. They will face off in the general election on Nov. 5.

Walsh, a state representative who lives in Dorchester, finished with 20,838 votes, 18.5 percent of the vote. Connolly, a City Councillor from West Roxbury, carried 19,420 votes, 17.2 percent of the vote, according to unofficial results released by the Boston Election Department.

The election has been the most competitive race that Boston has seen for years, in large part because Thomas M. Menino announced in March that he would not seek a sixth term after more than 20 years as city mayor, opening the door for an influx of new candidates. Twelve names were on the ballot Tuesday, including six minority candidates.

Extensive field teams likely helped Walsh and Connolly turn out voters to the polls.

Field organizers and volunteers have made a “very, very aggressive” push to contact Connolly supporters since Saturday, said Krishna Ghodiwala, deputy field director for the Connolly campaign.

Volunteers at a Connolly office in downtown Boston on Tuesday gathered at a windowless office suite strewn with empty pizza boxes, Dunkin’ Donuts cartons, and sheaves of paper to make calls and prepare for canvassing.

Both Walsh and Connolly have sought to differentiate themselves from a crowded field of candidates that often espouse similar stock and trade Democratic stances on social issues to cater to predominately progressive and liberal Boston voters.

Connolly has campaigned on a platform that revolves primarily around education.

A former schoolteacher, he has advocated for extending the school day and lifting the current limit on charter schools.

Ross Levanto, Connolly supporter and chair of the Ward 5 Democratic Committee, said that Connolly has managed to create a unique message that has pushed him ahead of his competitors.

“He has a message that really resonates with people who want to raise their families in Boston,” Levanto said.

Ghodiwala also claimed that Connolly was the first candidate to advance a comprehensive platform.

“He is as much a visionary as a nuts-and-bolts kind of guy,” Ghodiwala said.

For his part, Walsh’s campaign has been bolstered by union support. Walsh—who previously served as head of the Boston Building Trades, which represents ironworkers, electricians, and other unions—secured campaign supporters from labor groups and solicited donations from several union groups. He was endorsed by the Greater Boston Labor Council in June and later the United Steelworkers District 4 in September.

Walsh proposed in September a plan to sell City Hall Plaza in an effort to revitalize the area to generate funds from private resources and move the government services elsewhere. Walsh suggested the money gained could then be used for investment in education and parks in the city.

Walsh has also made housing issues a priority and plans to work with developers to expand affordable housing options in Boston’s neighborhoods.

—Staff writer Laura K. Reston can be reached at laura.reston@thecrimson.com. Follow her on Twitter @laurareston.