Vineyard Democrats broke ranks with the rest of the commonwealth this week, throwing their support to former U.S. Labor Secretary Robert Reich over state treasurer Shannon P. O'Brien in the primary race for governor.

Only Democrats in Oak Bluffs handed the majority vote to Ms. O'Brien, who won the party nomination Tuesday in a decisive victory over three rivals on a crowded ticket. The state treasurer will now oppose Republican Mitt Romney in what is expected to be a tight race for governor in November. A Democratic stronghold, Massachusetts has been under Republican rule since William Weld was elected governor in 1990. Mr. Weld was succeeded by Republican Paul Cellucci, who was succeeded by former Lieut. Gov. Jane Swift when he resigned to take a post as Canadian ambassador. The acting governor dropped out of the race soon after Mr. Romney announced his candidacy earlier this year.

Mr. Romney ran unopposed, but there was a contest for lieutenant governor on the GOP ticket, and here Vineyard Republicans followed the state trend, voting to support Kerry Murphy Healey over James Rappaport. In the race for lieutenant governor on the Democratic ticket, again Vineyarders bucked the trend, voting to support Lois Pines over Christopher Gabrielli. Mr. Gabrielli won the nomination.

Voter turnout was low on the Vineyard, as it was throughout the commonwealth. A total of 1,892 Democrats and 676 Republicans cast ballots in six towns on Tuesday, a classic early autumn day on the Island with sunny skies and warm temperatures.

Most polling places were quiet throughout the day. Early Tuesday morning in West Tisbury, more voting officials than voters trickled through the public safety building. One voter had a question: "This is my first time voting in Massachusetts. How does this work?" she said.

The woman at the check-in table replied: "Oh honey, this is easy. We're not Florida, you know."

In the Democratic race for governor Mr. Reich won 765 votes on the Vineyard to 626 for Ms. O'Brien. Senate president Thomas Birmingham trailed with 246 votes while fourth-place finisher Warren Tolman captured 203. Mr. Birmingham did even more poorly on Nantucket, where the local newspaper last week urged island voters not to vote for him because of his recent role enabling the restructuring of the Steamship Authority at the behest of the city of New Bedford. Mr. Birmingham is a summer visitor on Nantucket. By contrast, the senate president did extremely well in New Bedford.

In another interesting primary return, longtime New Bedford Rep. George Rogers, who is close friends with former city solicitor George Leontire and has been at the center of the bitter Steamship Authority war, lost his seat to challenger Mark A. Howland.

There were no other key contests on either ticket, but three Democratic candidates for county commission won the right to appear on the state ballot in November: incumbent Robert Sawyer and challengers William Shay and Paul Strauss. Mr. Strauss did well, ending as the top vote-getter overall in the county commission race and also in his home town of Oak Bluffs, where he captured 257 votes.

Ms. O'Brien won the party endorsement in June at the Democratic convention in Worcester.

Two Vineyard residents who attended the June convention as delegates appeared to reflect much of the sentiment caross the state this week, warmly endorsing Ms. O'Brien as the party candidate even though they did not vote for her.

Robert Sawyer, a member of the Tisbury town caucus, said the Vineyard delegation had initially voted to support Steve Grossman, a candidate who later pulled out of the race. Mr. Sawyer said he voted for Mr. Tolman.

"I had a difficult time deciding between Tolman and O'Brien. But I have no difficulty with O'Brien. Her values are Vineyard values and she will be a marvelous candidate," Mr. Sawyer said.

Linda Sibley, a member of the West Tisbury town caucus, said she, too, voted for Mr. Tolman. "I voted for Warren Tolman and my husband voted for Shannon O'Brien," Mrs. Sibley said, adding:

"When I was at the convention I was torn between the two of them, and I met Warren Tolman personally and was impressed by his sincerity. But I also was a supporter of Shannon O'Brien from years ago, and I think now that the Democrats will probably be well-served having nominated a woman.

"And by the way, I went outside this morning and peeled the Warren Tolman stickers off my car and put my Shannon O'Brien stickers on."