The Republicans swept to a new U.S. Senate majority on Election Day, but the party may have delivered its most crushing blows to the Democrats this year at the gubernatorial level.

The GOP flipped four gubernatorial seats -- ousting an incumbent in Illinois and seizing open seats in Arkansas, Massachusetts and, most stunningly, in solidly blue Maryland. The GOP shed one seat, in Pennsylvania, to the Democrats.

The Democrats dodged a bullet on Wednesday when Democratic incumbents pulled out narrow victories Colorado and Connecticut. As of 1 pm Wednesday, two states were still waiting on final results. In Alaska, an independent running with a Democratic lieutenant governor candidate was ahead narrowly.

MAP: Tracking the 2014 governors race results

Meanwhile, with the exception of Pennsylvania, the GOP was almost entirely successful defending its most vulnerable governors against strong challenges, including Rick Scott in Florida, Scott Walker in Wisconsin, Sam Brownback in Kansas, Paul LePage in Maine, Nathan Deal in Georgia and Rick Snyder in Michigan.

Republicans went into Election Day holding 29 governorships, to 21 for the Democrats. They've already reached 32, though that could slip back to 31 if incumbent Republican Sean Parnell loses in Alaska. The prospect of reaching 35 had been a real possibility earlier on Election Night, but receded somewhat after Democrats retook the lead in Colorado and Connecticut.

Even at 31 seats, the GOP would achieve a stunning degree of dominance on the state level, alongside the party's already strong lead in state legislative control (which is poised to increase by between five and eight chambers after the election results are settled).That would be the most governorships held by either party since the 1980s, and by the Republicans since at least the 1920s.

Even in some places where Republicans fell short, they did better than expected. In Vermont -- a governorship that many observers, including Governing, had ranked as one of the safest in the Democratic camp -- incumbent Peter Shumlin, the chairman of the Democratic Governors Association, failed to win a majority of the vote and will now need the legislature, which is controlled by the Democrats, to ratify his second term.

Some contests that had seemed close ended up surprisingly tilted toward the GOP, such as the bid for a second term by Walker in Wisconsin. He had been a polarizing figure in a deeply divided state, but he was leading by 5 percentage points Wednesday morning.

The prospect of a GOP wave in this year's gubernatorial races was always a possibility, but in the run-up to Election Day, it looked even likelier to be an anti-incumbent election.

In its final ratings, Governing considered fully half of the gubernatorial races to be competitive, and a striking 12 were considered tossups. Most of those were well within the margin of error in recent polling, and all but two involved incumbent governors rather than open seats. This suggested that a half-dozen or more incumbents from a mixture of the two parties could fall on Election Night.

With the possible exception of Parnell in Alaska, all the incumbent losers will be Democrats. In the tossup races, the GOP came close to running the table. Of the 12 tossup races, the GOP either won or was leading in 10 races.

Beyond Alaska, the Republicans lost only one tossup race -- in Rhode Island, where the Democrats held on to the governor's mansion. And none of the GOP's incumbents seemed to be in danger of losing -- even those that had been controversial, such as Brownback, LePage and Walker.

In addition, while a number of gubernatorial seats will switch partisan hands in 2014, the number will be smaller than two elections in the recent past. In 2002, a whopping 20 seats switched partisan control, and in 2010, 18 switched. In both of those cycles, however, Republicans won Democratic-held seats and Democrats won Republican-held seats, driving up the numbers of partisan flips. This time, the switches appear to be going only in one direction.