Kim Sinatra, former governor Bill Weld, and Robert DeSalvio, who will run the Everett hotel, prepare to testify.

The pugnacious Steve Wynn compromised just enough on Tuesday to win the support of a swing vote on the Massachusetts Gaming Commission and ended up walking away with a license to build a $1.6 billion Las Vegas-style casino on a heavily polluted plot of land in Everett.

By a vote of 3-1, the Massachusetts Gaming Commission chose Wynn over Mohegan Sun’s casino proposal at Suffolk Downs in Revere. The decision means thoroughbred horse-racing at uffolk Downs will probably end and it also sets the stage for an interesting battle of wills between Wynn and Boston Mayor Marty Walsh, who accused the commission of being biased in favor of Wynn and has threatened to sue.

Indeed, the lone holdout of the four commissioners, James McHugh, gave a slight edge to Wynn on the basis of the competing casino proposals, but he said he had much greater confidence that Mohegan Sun’s proposal would get built because of the political resistance to Wynn in Boston and nearby Somerville and the potential for long delays in resolving traffic congestion issues.

Wynn’s edge was his company’s strong balance sheet and his enormous success in Vegas and Macao. Wynn promised to invest more money in his Everett casino, pull in more gamblers from outside the region and, most important, hire more people. He promised 2,797 construction jobs compared to 1,579 at Mohegan Sun and he promised 4,382 resort jobs compared to 3,172 at Mohegan Sun. Even adding a generous number of Suffolk Downs jobs (1,133) to Mohegan Sun’s total, Wynn still had more jobs overall.

But Wynn is also a royal pain. Where Mohegan Sun worked cooperatively with and offered generous mitigation packages to Revere and its surrounding communities, Wynn played hardball. He went to arbitration on mitigation with Chelsea and Somerville and won. He angered Walsh so much during mitigation negotiations with Boston that the mayor pulled out of the process and left it up to the commission to protect his interests.

Wynn responded much the same way last week when one commissioner panned the design for his Everett hotel and two commissioners suggested his traffic mitigation efforts for Sullivan Square weren’t sufficient. He sent a letter to the commission on Friday evening defending his building design and blaming Boston’s “irrational demands” for the breakdown in communications. He refused to budge on much of the traffic mitigation, suggesting a provision assessing a fine on the company for each car that travels through Sullivan Square in excess of a certain level would be “an impossible business risk.”

But over the weekend his employees sensed their boss had miscalculated. They sent an email Monday morning saying Wynn was open to redesigning the hotel. And when the commission invited both companies to explain their positions Tuesday morning, Wynn significantly increased his investment in Sullivan Square and agreed to the per-car fines but with a cap on them of $2 million a year over 10 years.

Kim Sinatra, who in her gladiator stilettos added some flash to the crowd of white guys in business suits at the Boston Teachers Union headquarters in Dorchester, clearly swayed the commissioners by promising to redesign the exterior of the hotel and invest more heavily in a solution to congestion at Sullivan Square. Sinatra also promised that one of the company’s first calls if it wins the license will be to Mayor Walsh.

“It’s not in our interest to invest a billion-six and be left with a transportation situation that does not work,” she said.

Everett Mayor Carlo DeMaria and his wife, right.

Wynn had originally offered $46 million over 10 years. The commissioners had asked for more, including a penalty of $20,000 for each car traveling through the square to and from the casino in excess of a number to be determined at a later date. Sinatra said her boss saw the $20,000 fee as an uncapped liability. “We were uncomfortable with that,” she said.

So Wynn proposed putting up $56 million, and offering to pay $20,000 per car as long as those fines were capped at $2 million a year, or $20 million over a 10-year period.

The commission wanted Wynn to get all its permits for its ullivan Square short-term fixes from Boston by July 1, 2015, or face license revocation. Sinatra agreed to apply for the permits within three months of being selected, but said the company shouldn’t be held responsible if Boston refused to act on them. “Otherwise, quite frankly, we are putting ourselves at the mercy of Boston,” Sinatra said.

Former governor Bill Weld, who works at ML Strategies, which has been retained by Wynn, chimed in that the Las Vegas company was a blue-chip firm that the commissioners could rely on. He suggested that with all the focus on Sullivan Square, and the money Wynn is investing, now may be the time to finally get something done to deal with traffic there.

Commissioner Gayle Cameron, who initially led the charge among the commissioners on Sullivan Square traffic issues, was clearly swayed. “This was never about a dollar amount. It was about skin in the game. We’ve accomplished the job we set out here,” she said.

Winning her support changed the dynamics among the four commissioners. McHugh, clearly skeptical about Wynn’s mitigation efforts and the political obstacles to dealing with congestion issues, lost a couple of conditions he wanted to impose on a Wynn license and then found himself isolated when it came time to take a vote.

The commissioners overruled Wynn’s objections to a number of provisions (for example, they said Wynn must cover $750,000 of Boston’s expenses for determining the casino’s impact on the city, three times what Wynn wanted to pay) but overall they accepted most of the changes Wynn wanted in the licensing conditions and agreed to the dramatic changes in Boston mitigation payments.

Mitchell Etess, the CEO of Mohegan Sun, said he went into Tuesday’s meeting thinking the applicants were only being allowed to explain their earlier positions, not to change those positions. “They changed their deal this morning, which didn’t seem to be allowed,” he said of Wynn.

He also said the commission accepted Wynn changes in the licensing conditions that allow the company to abide by the principles of its casino application but not every statement in it. By contrast, Mohegan Sun was required to honor the commitments put in its license application. Etess said the change means Wynn is not being held to the job targets it promised, although McHugh said after the decision that the company will be held to those numbers.

“I hope for the Commonwealth’s sake they have to live up to those numbers,” Etess said. “That large disparity seemed very, very unlikely.”