Anne Anderson exiting the Rayburn House Office Building with Irish Prime Minister Enda Kenny, right, along with security and Irish government staff members after meeting with members of Congress. (Marty Katz)

The running of the green began when Anne Anderson woke before dawn Friday for her first celebration of St. Patrick’s Day as Ireland’s ambassador to the United States.

“I thought I was prepared,” said Anderson, who took up her post six months ago. “Of course, logistically I was prepared because that’s what a good ambassador and embassy does. I was not prepared for how it actually felt on the day.”

Washington’s official observance was Friday, not March 17, because Congress isn’t in session this week. So that was P Day, and the ambassador spent 18 hours escorting Irish Prime Minister Enda Kenny on his annual goodwill trip around the nation’s capital.

It was exhilarating. It was exhausting. And it was a little overwhelming, she said, to see firsthand how much Ireland and the Irish people matter to America’s political leaders. “There was an enormous sense of pride that a country of our size, less than 5 million people, could have the impact that we clearly have on the United States.”

Anderson’s shamrock race:

8:30 a.m., breakfast with Vice President Biden: Top of the morning at the Naval Observatory, where the vice president hosted the Irish delegation and guests with eggs, potatoes and Irish soda bread. The mood was intimate and festive: The Irish Catholic Biden, who was honored at an American Ireland Fund dinner Thursday night, spent 24 hours quoting his late mother, Catherine Eugenia Finnegan Biden, and repeating old Irish sayings, to wit, “A good friend is like a four-leaf clover: Hard to find and lucky to have.”

10:30 a.m., the Oval Office: Anderson et al went by motorcade down Massachusetts Avenue on their way to the White House, where President Obama and Kenny discussed global economics, immigration reform and Ukraine. Ireland is honored with the equivalent of a state visit every year (meetings, lobbying, honors, publicity and general goodwill), something no other nation can claim. “Throughout the day, the mood was very festive, but there was very serious business done,” Anderson said.

Celebrating St. Patrick’s Day, originally a religious holiday in Ireland, is an increasingly big deal in Anderson’s home country. But there’s nothing quite like the American version — a day-long party for the 35 million Americans who claim Irish ancestry, and an excuse for everybody else to knock off work early and drink. Everyone is Irish for the day, which is always good news for Irish politicians, Irish businesses and Irish tourism.

Noon, lunch at the Capitol: Green ties everywhere! House Speaker John A. Boehner (R-Ohio) hosted the traditional bipartisan congressional lunch for the prime minister, with Obama and Biden in attendance. Almost all the leadership attended; the meal ended with a banjo and guitar performance of Irish folk songs, including “Wild Rover.” Kenny, Anderson and Team Ireland switched gears and did some serious lobbying on the Hill.

5 p.m., White House reception: Green dresses everywhere! Anderson raced to her residence for a quick change — from business attire to a green sheath dress and suede high heels — before the party in the East Room, where she joined first lady Michelle Obama, who was also in green. Kenny presented the annual bowl of shamrocks to the president, a tradition dating to Harry Truman.

“Once again, today is not technically St. Patrick’s Day,” Obama told the Irish American VIPs. “And once again, none of you seem particularly bothered by this. At least you’ll have a weekend to recover.”

Amid all the talk of Irish friendship and resilience, the ambassador got a shout-out from the father-of-two-girls leader of the free world. “I want to extend a special welcome to Anne Anderson, the newest ambassador of Ireland to the United States,” he said in brief remarks. “Anne is the first woman to hold this esteemed position . . .” — the crowd applauded, and Obama delivered his punch line — “. . . which means that they might finally get it right.”

7 p.m., embassy party at the Fairmont Hotel: The bars were packed, the stout flowing and the Irish cheeses scarfed down by a crowd too big to fit into the embassy, which is why they squeezed into the hotel ballroom. Anderson gave the “warmest of Irish welcomes” to her guests, telling them: “Today has been extraordinary. I’m certainly on a high, and I think the whole delegation is on a high. Washington has truly opened its arms to us today.”

After Kenny gave yet one more pep talk about the Irish economic recovery, everyone mingled for chitchat and photo-ops. In the crowd: Anderson’s significant other, surgeon Frank Lowe, down from New York to join the fun.

9 p.m., private dinner at the ambassador’s residence: The finish line, where a small number of guests ate, drank and, we presume, tried to stay awake.

Saturday was the designated day to recover. Sunday, they all headed up to Boston for a day of parties; Monday, they’re scheduled to be in New York for breakfast with Mayor Bill de Blasio at Gracie Mansion, Mass at (where else?) St. Patrick’s Cathedral and the parade on Fifth Avenue.

Lesson learned for next year: “I might wear more comfortable shoes,” Anderson said with a laugh.