Bill Murray, Brooklyn Bartender

Many restaurants host an evening for friends and family before a formal opening as a dress rehearsal for the real thing. Such was the case on Sept. 16 at the Brooklyn bistro 21 Greenpoint, formerly known as River Styx. It was reopening, under the same owners, with a new menu and a new look.

Most friends-and-family nights are intimate affairs. Not this one. There were camera crews on the sidewalk and a line of people stretching from Greenpoint Avenue nearly to the East River.

The restaurant’s co-owner, Homer Murray, had let it be known that there would be a special guest bartender on duty that night: his father, the actor and urban folk hero Bill Murray. But at 7:15 the 65-year-old star of “Ghostbusters,” “Groundhog Day” and “Lost in Translation” had yet to arrive for a shift scheduled to begin at 7.

From inside 21 Greenpoint, the younger Mr. Murray and the restaurant’s bar director, Sean Patrick McClure, a veteran of Le Bernardin and Dirty French, kept an eye on the growing crowd. Asked to describe his father’s bartending skills, Mr. Murray said: “He just kind of pours Slovenia Vodka into people’s glasses when they look thirsty. He’s about efficiency. Turn-and-burn.”

The throng seemed to press against the doors shortly before 7:30, and the owner decided to open for business, although the main attraction had yet to appear.

At 8:05, Bill Murray stepped in at last. The place lit up with smartphone flashes as he moved toward the bar. Those not occupied with capturing his likeness for their Instagram accounts gave him a round of applause.

His first order of business was to grab a bottle of Slovenia Vodka from behind the bar. He twisted off the square black cap, poured a shot into it, drank it and placed the cap on his head to big cheers. Then he got to work.

People who shouted the names of complicated cocktails got nowhere fast. But when someone said, “Mezcal, rocks,” the guest bartender served it up chop chop. Mr. Murray was equally quick with tequila shots, for himself and for anyone who asked.

As he went about his business, he sang along to the music — “Disco Inferno,” Stevie Wonder’s “Higher Ground,” The Rolling Stones’ “Miss You” and “Street Fighting Man.”

One man asked him if he knew how to make a Bellini.

“I know people who do,” Mr. Murray said.

He refused another man’s order until, at Mr. Murray’s request, the guest removed his hat.

Mr. McClure had whipped up a cocktail in honor of the restaurant’s reopening, mentioning that he had yet to come up with a name for it. Mr. Murray took a sip of the drink, eyes closed. Then he turned to Mr. McClure and said, “The Depth-Finder.” And so it shall be known. (Recipe below.)

The orders kept coming. Smartphones kept flashing. Mr. Murray slid a bourbon shot toward one patron, saying, “Old Grand-Dad will make you feel more intelligent.”

When a fellow bartender was in the middle of making a cocktail, Mr. Murray swiped the jigger and drank its contents.

A bit later, he said, half under his breath, “I’m making nothing in tips.”

A group of firefighters entered the place, hoping for a photo with the special guest. Mr. Murray took a pineapple from the bar and cradled it like a baby as he posed with them.

As the evening wore on, he left his station briefly and nearly bumped into a young woman. As if to make up for his lapse, he put his hands on her shoulders, kissed her on the nose and told her she was beautiful.

Around 10, the music cut off, and Mr. Murray gestured toward the co-owner with the drink he held in his hand.

“This is my firstborn son, Homer,” he said. “And I am so happy for myself, and his brothers and sisters and mom, and all of you, that he has not continued in the family business. Instead, he has taken the joy of the family — to have a drink, and to have a meal, and to have friends together in one place — and made it his life’s work. To my son, and his friends, and his work, and all his partners. Homer Murray!”

More cheers from the crowd.

Mr. McClure praised Mr. Murray’s performance. "A mixologist simply knows how to mix drinks,” he said. “A bartender knows how to run a bar: interact with guests, have fun, have conversations with them. Bill is a bartender.”

Mr. Murray looked fatigued toward the end of his shift. When asked what he had learned on the job, he said, “Well, if your barback isn’t getting you the right glasses” — he glared at a fellow bartender — “then you’re put in an instant of creativity, where you have to make a drink with the glasses you have. And that, to me, is a life of service.”

The Depth-Finder

1 1/2 ounces Slovenia Vodka

3/4 ounce Amaro liqueur

3/4 ounce fresh lemon juice

2 ounce soda water

1 pinch dried rosebuds

Pour the vodka, Amaro and lemon juice into a shaker with ice. Shake vigorously, and strain into a highball glass.

Top with ice, soda water and garnish with dried rosebuds. Serve with a straw.