On Sunday night, Matt Williams devoured dinner at an Italian restaurant, retreated to his hotel room, lay in bed and found sleep futile. “Nervous energy,” he said. “That’s part of the deal.” He had never managed a major league game before, and all possibilities rattled around his head. Whatever stresses he conjured could not have matched reality, could not have competed with the catch-your-breath, flip-your-stomach moments the Washington Nationals presented him with the first day on the job.

On a chilly, sun-drenched afternoon at Citi Field, the Nationals won Williams’s debut, 9-7, against the New York Mets. The Nationals did not hold the lead until the 10th inning, when Ian Desmond lifted Jeurys Familia’s two-strike slider to center field for a sacrifice fly. Two batters later, Anthony Rendon celebrated his first opening day with a three-run homer off former National John Lannan. To reach that point, Williams and the Nationals endured maddening twists, blissful highs and sickening blows.

“I’m alive, yeah,” Williams said. “Right in the thick of it.”

The celebration in the Nationals’ clubhouse was muted by the worst moment: Catcher Wilson Ramos, whom Williams tabbed as his cleanup hitter, believed he broke his left hand on a foul tip, according to a person familiar with the situation, and left before the seventh inning. Williams said initial X-rays came back negative.

The day’s other events paled in magnitude, but the game gave Williams plenty of them. In the second inning, Williams rushed to the middle of the diamond, where Bryce Harper lay supine on the infield dirt — his head had collided with the shin of the Mets’ Eric Young Jr. as he slid into second base. Harper stayed in the game, and he stood in left field in the bottom half of the inning as Williams’s ace, Stephen Strasburg, gave up his fourth run in the year’s first two innings.