Special elections in the Bay State might not be that special anymore.

Democratic Rep. Edward J. Markey defeated GOP nominee Gabriel Gomez in Tuesday’s special election for former Sen. John Kerry’s seat. His victory kicks off yet another special contest to fill the seat he’ll vacate in the 5th District — the third special election in as many years in Massachusetts.

Starting months ago, a handful of Democrats announced their candidacies for this imminent House race. That’s because, in part, open seats are rare in the commonwealth’s congressional delegation. Markey held his deep-blue seat in the Boston suburbs since 1976.

Among the crowded field, there are two front-runners: state Sen. Katherine Clark, who has eyed the 5th District since Markey indicated interest in the Senate special election, and Middlesex County Sheriff Peter Koutoujian, who served in the state House before his current gig.

Clark is the prohibitive front-runner, according to Democrats. She started organizing and fundraising early and filed her paperwork to run on Feb. 19, months before Markey won the Democratic Senate special primary on April 30.

Clark’s early start gives her a financial advantage over her opponents. She reported $261,879 in campaign contributions after the first quarter of the year, a total she’s poised to add to when the next filing deadline rolls around June 30.

She also has support from EMILY’s List, which has put her “On the List” of its top candidates. It’s a key advantage in special elections, which are much shorter contests than general elections.

“Money wins these things,” Jim Spencer, a Massachusetts Democratic operative, said of special elections.

Operatives said Koutoujian’s popularity in the district — he was re-elected to the sheriff job in November with 77 percent — and his ties to law enforcement make him a formidable candidate as well.

They also argue that Koutoujian’s viability will be more clear after he files his first fundraising report following the June 30 deadline. He’s had a month to raise funds for the contest; he filed federal paperwork to run for the seat on May 22.

“He may have at the outset an initial advantage because [the sheriff’s office] is a county office, so it’s a bigger footprint,” state Democratic strategist Mary Anne Marsh said. “And he may have more of an organizational advantage, but that remains to be seen.”

Other announced candidates include Carl Sciortino, an openly gay state representative who has strong progressive roots, and state Sens. Karen Spilka and Will Brownsberger.

While operatives said all of these candidates are formidable, they noted that the rest of the field will have a hard time matching Clark’s early fundraising advantage.

No Republicans have filed federal paperwork for the seat. But any GOP candidate would have a hard time winning in this heavily Democratic district that President Barack Obama carried with 65 percent in 2012.

Democrats expect that whoever emerges from the primary will be the next member of Congress.

Officials will not call a special election until Markey officially resigns from the House. A Democratic aide said Markey is scheduled to be sworn in to the Senate shortly after the July Fourth recess.

After he resigns, state election law dictates officials must schedule a special election to be held in 145 days to 160 days. That would mean a late-summer primary and November special election.

For voters in the 5th District, this latest contest continues the near omnipresence of political campaigns in their area. Democratic strategists in Massachusetts say, however, voters are not likely to be fatigued by the constant campaigning.

“This is Massachusetts,”  Spencer said. “We only have three pastimes: sports, politics and revenge.”

Correction: 4:24 p.m.

This post has been corrected to reflect that the Progressive Change Campaign Committee has not endorsed Carl Sciortino.