NEW YORK — After the frustration and the waiting; after the nerves and last year’s bitterness, it suddenly looked easy for Marin Cilic.

See ball. Hit ball. See opportunity. Seize opportunity.

He has never had a bigger one on a tennis court, and the 6-foot-6 Cilic truly did not flinch: walking tall into Arthur Ashe Stadium and playing taller as he swept to the U.S. Open title with a 6-3, 6-3, 6-3 rout of Kei Nishikori.

“Everything I was working for and dreaming came today,” said Cilic, a 25-year-old Croat. “And I feel for all those other players who are working hard, this is a big sign and big hope that if you are working hard things are going to pay off.”

A year ago, Cilic missed the U.S. Open because he was serving a suspension after testing positive for a banned stimulant. Though he faced a two-year ban, he appealed, arguing that he had unintentionally ingested the substance in a glucose tablet, and succeeded in having the suspension lifted after four months.

He returned to the tour in October and rose in the rankings. He arrived in New York seeded 14th and with two titles already to his credit in 2014. But it would have taken quite a soothsayer to predict that from that platform, he would claim the Open trophy in a men’s tennis era when outsiders have so rarely managed to reach the finish line at major tournaments.

“I think the stars crossed,” Cilic said in a postmatch interview on CBS, mixing the metaphor but still making an essential point, because a star has certainly made a big difference for Cilic.

Goran Ivanisevic, the big-serving and charismatic Croat, became Cilic’s coach late last year and has clearly brought both expertise and positive energy to his countryman.

“We are working really hard, but the most important thing he brought to me was joy in tennis and always having fun,” Cilic said.

Now, both the coach and the pupil have one Grand Slam singles title apiece. Ivanisevic earned his in a strange-but-true fashion, too, winning Wimbledon in 2001 as a wild card in a final pushed to Monday because of rain.

“I guess Mondays are special for Croatians,” said Cilic, who had 17 aces in the match.

It was the first Grand Slam singles final for Nishikori and Cilic, but only the 10th-seeded Nishikori did a fair impression of a rookie, and a rather weary rookie at that.

“I was a little bit tight and nervous,” Nishikori said. “So many things to think about. I was trying to concentrate, but it wasn’t enough, I guess.”

“Couldn’t fight one more match,” he added.

Nishikori said the match had been one of his worst of this tournament, adding, “But also, he was very aggressive and very fast.”