SAN DIEGO — With his back to the harbor and Coronado Island on a picturesque late Southern California morning, Aaron Boone’s face was painted with contentment Wednesday on the Manchester Grand Hyatt balcony.

Why wouldn’t he look so satisfied?

Tuesday night, the Yankees signed free agent right-hander Gerrit Cole to a record-breaking, nine-year deal for $324 million that put the best pitcher available atop the Yankees’ rotation.

So, ahead of the deal becoming official after Cole takes a physical on Monday with a press conference likely Tuesday at Yankee Stadium, Boone gushed about his newest toy.

“You are talking about a guy who is the best of the best,” he said of Cole, who went 35-10 with a 2.68 ERA in 65 starts the past two years for the Astros and is 94-52 with a 3.22 ERA in 192 big-league starts. “A guy certainly in the prime of his career. We are talking about a great, great player. We are seeing a guy who is really talented, really good at his craft, really intelligent and now has the experience at 29 in the prime of his career. This is what greatness looks like.”

According to William Hill sportsbooks, Cole’s signing moved the Yankees from a 5/1 pick to win their first World Series since 2009 to 3/1 after winning 103 games a year ago when Cole was an Astro, former Yankees ace Luis Severino pitched a dozen innings, Dellin Betances worked two-thirds of an inning and left fielder Giancarlo Stanton played in 18 games.

When Cole hit free agency following the Astros’ loss to the Nationals in Game 7 of the World Series, the Yankees, Dodgers and Angels were installed as the favorites to get him.

According to a person with knowledge of the situation, several teams made offers north of $300 million, but Cole’s promise of not having a “West Coast bias’’ about leaving his Southern California roots was real.

“I wasn’t surprised by the signing. I knew Cole was someone the organization really wanted. He’s a premier starting pitcher and pairing him with the guys we already have, makes our rotation and whole pitching better,’’ Yankees reliever Zack Britton told The Post in an email. “I only know Cole through my agent [Scott Boras]. Hoping to reach out when it’s all official.’’

Those who know Cole from his days with the Pirates and Astros believe New York won’t make the same kind of dents in him that other players have absorbed playing under the intense pressure that comes with the big contract and the Yankees’ uniform.

Boone, who said he hadn’t talked to Cole as of late Wednesday morning, joined that chorus after a long meeting with Boone last week in Orange County, Calif.

“I think he will thrive,’’ Boone said. “His greatness for one thing, the mindset. We spent a lot of time together and learned about him and him about us. Everything suggests this is a guy who could thrive anywhere but especially New York.’’

GM Brian Cashman agreed.

“I would use the example how he is willing to bet on himself. I don’t think many high school kids drafted in the first round by their childhood dream team with financial components coming their way that far exceed what a college scholarship would be worth saying, ‘I am going to college,’” Cashman said.

“Going through six years with two franchises and not be open to extension and go see what it is going to like in free agency. Those are examples of someone talking the talk and shows he can walk the walk.’’

And, if possible, grow as a pitcher.

“Hopefully you are finishing off a team that can win a championship,’’ Boone said. “It’s an elite talent, elite makeup.’’