BRUSSELS — European leaders on Friday were toasting British Prime Minister Boris Johnson's thumping election victory, embracing the decisive result for a man who campaigned for Brexit and against much of what they stand for.

The counterintuitive celebration stemmed from Europe's resignation that Britain's split from the European Union was inevitable, and from E.U. frustrations with more than three years of dealing with British leaders who were barely in control of their own Parliament.

Now Britain is expected to leave on Jan. 31 and enter an 11-month limbo state, in which little will change in the day-to-day lives of U.K. and E.U. citizens. Britain will still be subject to E.U. rules and will be able to trade with Europe as if it were a full-fledged member.

But leaders will have to make a furious dash to reach a trade deal and work out their post-Brexit relationship before Dec. 31, 2020, when the transition period is set to end. Failure could mean the same jump-off-the-cliff breakup that both sides have said they dearly want to avoid.

As European and British leaders prepare to embark on those tricky negotiations, the European side hopes the size of Johnson’s win will enable him to deliver on the deals he makes in the bargaining sessions — and protect him from being taken hostage by Brexit hard-liners who favor only the most severe breakup.

“To be honest, many of my counterparts were pleased at the fact that this was a clear outcome, that we’re not again facing a situation with a hung Parliament where you can’t make headway in either direction,” said German Chancellor Angela Merkel, who rarely speaks so openly about the internal politics of other countries.

“I have to pay my respects. Chapeau, one can only say, that he has managed to achieve this result,” she said, with a flicker of a smile.

But she acknowledged the tension in the talks that are expected to start soon after Britain’s formal exit from the bloc. Germany and others want to preserve the strongest ties possible with Britain — but the more Johnson chooses to diverge from E.U. rules, they say, the tougher the restrictions they will impose on British businesses.

“We will have a competitor on our doorstep now, a country that is no longer a member of the single market,” Merkel said. “Great Britain will have to carefully weigh the advantages and disadvantages” of diverging from E.U. regulations.

French President Emmanuel Macron also delivered a stark warning to London.

“My message to the British is that the more loyal we are to each other, the more our relationship will be close. But don’t think you can have an extensive trading relationship, a maximal access to the European market, with substantial differences on sanitary, climate, economic and social regulations. This is not true,” he said.

If Johnson wants “a very ambitious trade deal, then the regulatory convergence must be very ambitious. It is easy. Be my guest,” he said.

Over the next year, negotiators are somehow supposed to hammer out a major trade deal, as well as agreements about how Britain and Europe cooperate on security, foreign policy and a range of other issues. Virtually no one on the European side thinks it is possible to agree to a meaningful trade deal that quickly — meaning either Johnson will have to break a campaign promise by asking to extend the transition, or Britain and the E.U. could wind up with the same type of sudden break at the end of 2020 that Parliament until now refused to allow.

Leaders are uncertain which approach Johnson will take, since he entered Downing Street in July with bombastic and uncompromising rhetoric, but then backed off some of his red lines in negotiations over a withdrawal deal — and requested a Brexit extension he had earlier denounced.

Europeans also are unsure how hard Johnson will push for British autonomy and want to diverge from E.U. rules and regulations.

That was one of the main themes of his “take back control” Brexit referendum campaign. But he said little about it in the general election.

Because divergence could lead to economic pain for many British businesses — and for many of the new supporters he picked up in old Labour heartlands — many in Europe are hopeful he will ultimately choose a closer relationship.

Analysts said one clue may lie in the origins of Johnson’s opposition to the E.U. Yes, he wrote anti-E.U. screeds as a newspaper correspondent based in Brussels. But he was reportedly conflicted on Brexit — writing two versions of a 2016 opinion column, one embracing Europe, the other rejecting it. And ultimately his choice may have had more to do with his political aspirations than with ideology.

Johnson has been “pragmatically anti-Europe because he thought it would win him the leadership of the Conservative Party,” said Michael Cox, an emeritus professor of international relations at the London School of Economics. “His notion of what is Brexit could be quite a pragmatic outcome.”

Any trade deal is likely to require a number of politically unpalatable decisions for Johnson, who will find that E.U. negotiators are insistent on closely aligned regulations in exchange for access to their vast market. Britain is deeply integrated into the E.U. market, because until now it has been a full member.

“It will contain many things he will have problems with,” said Fabian Zuleeg, the head of the European Policy Center, a Brussels-based think tank. “That is going to be a bit of a shock for the U.K.”

It wasn’t just European leaders who, in the landslide victory for Brexit, saw signs that the broad majority could actually lead to a softer split.

Nigel Farage, leader of the hard-line Brexit Party and host of a radio talk show, said Friday that he was happy that at least some version of Brexit would be happening — and that Johnson’s victory is “far better than the alternative,” a win by the socialist Jeremy Corbyn, leader of the Labour Party.

But Farage said he does not believe Johnson’s Brexit will be what the people voted for. He said he still believes Britain should crash out of its long partnership with Europe without a deal.

“Does it get Brexit done? Er, no,” Farage told ITV News. “I think we’re probably going to head into three years of pretty agonizing negotiations.”

Farage warned his followers that the bigger the Conservative majority in Parliament, the less influence the most hardcore Brexiteers and euroskeptics will have on Johnson. With a majority of 40 seats, Johnson won’t need every member of his party to vote for his measures. A couple of renegades in his own party will not be able to stop him, or make oversized demands, the way they did before.

And Farage’s Brexit Party appeared to be in meltdown. It got 2 percent of the total vote on Thursday, winning zero seats in Parliament. Because the party will lose its seats in the European Parliament on Jan. 31, assuming Britain leaves as planned, it will be diminished as a force in British and continental politics.

Brussels is delighted to say adieu to what it regards as obstructionist rabble.

Booth reported from London. Karla Adam in London and Quentin Ariès in Brussels contributed to this report.