Voters in a wide swath of the South Shore, a part of the state friendlier to Republicans than elsewhere, elected Republican Patrick O'Connor to the State Senate Tuesday to keep one of six red seats in GOP hands.

Weymouth, Hingham, Cohasset, Scituate, Norwell, Hull and Marshfield went to the polls to replace Bob Hedlund, the Weymouth Republican who gave up his seat to become one of only seven GOP mayors in the state.

Democrat Joan Meschino, an attorney, CEO and former Hull selectman, lost out to O'Connor, the president of Weymouth's Town Council. The stretch of coastal communities from Weymouth down to Duxbury is one of the friendliest parts of the state to the GOP. O'Connor had great success on a funding level, doubling Meschino's total campaign warchest, and even has the support of several labor unions, including the AFL-CIO.

O'Connor told WGBH News Tuesday afternoon that when in office, he'll concentrate on state-funded efforts to combat the opiate epidemic.

"This is an issue we've been dealing with and I think that we need to double down on our efforts to make sure we have the community-based support systems for those who are struggling,"

Two other races for the Legislature - a House seat in Lynn, as well as a Senate seat in East Boston and just north of the city - will be won by Democrats today since no Republicans are running.

But today may not be the end of the fight for Hedlund's former Senate seat. Meschino already has enough signatures for a rematch on the November ballot, when droves of voters will come out to participate in the presidential election. That is, if Meschino manages to win the Democratic party primary and face off against the incumbent O'Connor in November, when Hillary Clinton and Donald Trump will presumably top the ticket..

"It'll be a much bigger electorate, there will be very short of time for whoever is in the seat to be able to create a record and prove their capacity, but it's going to be a huge turnout election," Senate President Stan Rosenberg, a supporter of Meschino, told reporters Tuesday.

The South Shore race is one of the few active competitions between competitive Republicans and Democrats, but two primary election fights worth keeping an eye on are shaping up in Cambridge and Somerville and on Cape cod.

Veteran Sen. Pat Jehlen (D-Somerville) faces a challenge for her seat from Cambridge City Councilor Leland Cheung. Cheung, who ran unsuccessfully for Lt. Governor in 2014, is pressuring Jehlen to disclose campaign donors monthly, far more frequently than that's required of legislative candidates under the law.

“The facts are that since first running for State Senate 11 years ago, Senator Jehlen has raised more than a third of her itemized contributions from PACs and lobbyists and another $50,000 in unitemized contributions from donors whose names aren’t publically available. It’s unacceptable that we don’t know who those donors are," Cheung wrote in a statement bashing Jehlen.

Jehlen is a progressive favorite from the very progressive reaches of Camberville, and with five terms under her belt, will be tough to out- campaign at the grassroots level. Cheung is well-funded, but has an uphill climb ahead of him to oust an intrenched incumbent.

On the Cape, Sen. Dan Wolf's (D-Harwich) decision not to seek a third term opened the field for several Democrats to jump into the fray to succeed him, including Rep. Brian Mannal (D-Barnstable,) former staffer at the Department of Mental Health Julian Cyr and current Barnstable County Commissioner Sheila Lyons.