Three months ago, American Airlines was accusing Mayor Rahm Emanuel of favoring its archrival by awarding hometown United Airlines five additional gates.

American Airlines was alone among airlines in objecting to a new lease agreement — threatening legal action that could have grounded Emanuel’s massive O’Hare Airport expansion project — only to sign on after the city made a hazy promise to speed construction of three common-use gates that favor American.

On Friday, Emanuel and American CEO Doug Parker joked about that political turbulence as they officially opened the first new gates at O’Hare in 25 years.

“I think I can speak for Doug, who I’ve known for years. I don’t think a month ago he would have predicted that the two of us would be standing here together,” the mayor said as the movers-and-shakers assembled at O’Hare laughed out loud.

Emanuel called Parker a “tough negotiator,” whom he “respects immensely” because he’s the same way.

“I want to thank Doug for his tough negotiations. For interrupting a lot of family dinners appropriately, saying, ‘I’d just like to have a few words with you.’ Thirty minutes later, [I was saying], ‘Doug, I’d like to get a word in edgewise,'” the mayor said.

“But when he sees a goal line, this is a guy who drives towards it.”

Parker picked up on the comedy routine.

“I actually was confident we’d be here a month ago together ’cause I knew you’d come to your senses,” Parker joked.

“Any rebuttal?”

Turning serious, Parker called Chicago an “incredibly important market for us.” Business here is “booming” with more seats being offered on American flights this summer than at any time in the last decade, he said.

“Last summer, we added service to Barcelona. Last week, we began service to Venice and Vancouver. And later this year, we’ll get service to Hawaii and to four destinations in the Caribbean,” Parker said.

“Our investment isn’t limited to construction of new gates. We’ve made a large investment for our premium customers with a new flagship lounge and renovated Admirals Club. And later this year, we’ll open up a new hanger and ground equipment maintenance facility.”

Aviation Commissioner Ginger Evans said O’Hare desperately needs “modern infrastructure and more gates. Many more gates.”

“These five gates will go a long way in improving service across the board for O’Hare with better on-time performance and more choices,” she said.

Noting that fifteen “new international flights” have been added at O’Hare since Jan. 1, the commissioner said, “We are stressing the facilities. We’re doing it on purpose. We have to build the revenue that we need to generate [to bankroll] that new generation of growth for O’Hare.”

The $78 million plan to add five new gates at O’Hare Terminal 3 was approved by the City Council two years ago. It’s not part of the, now $8.7 billion O’Hare expansion project approved in late March.

The 41,000 square-foot “L Concourse,” also known as a “stinger” includes new restrooms, concessions and waiting areas.

The 20-month-long project will allow O’Hare’s second-largest carrier to increase capacity, improve on-time performance and use regional jets with seating for 75 passengers to serve the regional and Midwest markets.

Emanuel called it the start of something big on, what was, somewhat fittingly, the final day of the old airline lease agreement that tied the city’s hands and ceded too much power to major airlines to determine O’Hare’s future.

“Today, as we cut the [ribbon] on the first new gates in 25 years, begins the starting point of a whole new chapter and a new era in Chicago’s economic growth and job creation,” Emanuel said.

“New runways, new terminals, new gates, new concessions….As Chicago invests in its future in transportation, it will write its future going forward.”

Without mentioning the decision Chicago voters will make in a mayoral election now just over nine months away, the mayor said, “The decisions we make in the next two-to-three years will determine Chicago’s place over the next 20-to-30 years.”

Before Friday, the price tag on the 60,000-job O’Hare expansion project was pegged at $8.5 billion. Evans upped the ante to $8.7 billion after airline projects that had been “pending approval” got final sign-off.