Democrats put up an unexpectedly strong fight as results rolled in from US midterm elections that will decide which party controls Congress, even as Republicans led by governor Ron DeSantis notched up a string of convincing victories in Florida.

The early tallies from the midterm elections on Tuesday showed many battleground races across the country were too close to call, with control of the Senate remaining in the balance and Republicans struggling to secure widespread victories in swing districts in the House of Representatives.

“It’s not a wave for sure,” said Lindsey Graham, the Republican senator from South Carolina, referring to the “red wave” that many pollsters had predicted heading into election day. However, Graham said his party was on course for a “very good night” and predicted it would win a majority in the lower chamber of Congress.

Frank Luntz, the Republican pollster, told the Financial Times: “This is not a tsunami . . . I think that Republicans got ahead of themselves.”

The best early result for Republicans was in Florida, where DeSantis, seen as a probable contender for his party’s presidential nomination in 2024, was quickly projected to win re-election along with senator Marco Rubio.

“I look forward to the road ahead,” DeSantis said. “We have accomplished more than anybody thought possible four years ago. But we have got so much more to do, and I have only begun to fight.”

Luntz called DeSantis “the real winner” of Tuesday night. “He has turned a successful governorship into a nationwide movement. I think he is going to give [Donald] Trump a run for his money.”

However, despite the strong showing in Florida — which had until recently been seen as a swing state — the results were more mixed in other battleground contests. Pivotal Senate races in Georgia, Arizona and Nevada remained exceedingly tight, with highly uncertain outcomes.

In Pennsylvania, Democrat John Fetterman won the Senate seat being vacated by the Republican Pat Toomey, despite having been hampered on the campaign trail by his recent stroke.

The White House said President Joe Biden had sent Fetterman his congratulations by text message.

Fetterman campaigned as a working-class progressive, wearing a goatee beard and almost always appearing in a hoodie and shorts. “This race is for the future of every community all across Pennsylvania,” he told supporters. “For every small town or person that ever felt left behind.”

Democrats held on to several bellwether House districts on the east coast where their candidates were seen as vulnerable, with victories for Abigail Spanberger in Virginia and Seth Magaziner in Rhode Island.

Meanwhile, New York governor Kathy Hochul was re-elected after holding off Republican challenger Lee Zeldin. The result will bring Democrats some relief after polls showed Zeldin closing a yawning gap in recent weeks with a relentless focus on crime.

Republicans only need a net gain of five seats to win a majority in the House and still have the edge in the lower chamber but they may assume control with a smaller margin than they hoped.

In a delayed victory speech delivered at 2am, Kevin McCarthy, the Republican leader in the House of Representatives, said: “When you wake up tomorrow we will be in the majority and Nancy Pelosi will be in the minority.”

The White House, which had been bracing itself for heavy losses in the House, said Biden had started to call Democrats including Spanberger and Senate majority leader Chuck Schumer to congratulate them on winning their races.

Even a small majority in the House for the Republicans threatens to stymie the next two years of Biden’s presidency. Republican leaders have suggested they will use the debt ceiling as leverage to push through their own policy priorities, such as cuts to federal spending.

They have also indicated they will disband Democrat-led investigations, including the special committee probing Trump’s role in the January 6 2021 attack on the US Capitol, and launch their own inquests into everything from the origins of the Covid-19 outbreak to the business dealings of Hunter Biden, the president’s son.

Republicans notched a number of high-profile wins outside of Florida too, with Greg Abbott, the Texas governor, winning re-election, and JD Vance, the former venture capitalist and author backed by Trump, winning his Senate race in Ohio.