Thursday morning, Jim Riggleman told his son, his mother and his brother to prepare for what he knew would happen later in the day. Riggleman drove to Nationals Park for the 312th game of his tenure as the manager of the Washington Nationals, resolved to end months of smoldering frustration about his tenuous contract status, even if it cost him the job he loved.

Riggleman had managed the Nationals to a .500 record, but working without a guarantee beyond the end of this season had become untenable for him. He met with General Manager Mike Rizzo 45 minutes before the first pitch. Riggleman wanted the assurance of a conversation, to take place Friday in Chicago, regarding the contract option held by the team for the 2012 season. If not, Riggleman told Rizzo, he would not board the team bus.

“I thought when I told him I wanted to talk, it probably was going to be over,” Riggleman said. “I’m 58. I’m too old to be disrespected.”

So two phases of Riggleman’s life came to an end Thursday, a bizarre day that stunned the franchise and brought both sadness and resolution for Riggleman. He no longer manages of the Nationals, and he no longer lives with the resentment he has felt since October, when he realized the Nationals were not going to exercise the option for the 2012 season.

The decision saddened Riggleman, but he believed it was the right thing to do, that a major league manager, especially one with more than 11 years of experience, should not operate on a one-year contract. He knew if his decision reached the highest level of the Nationals organization, owner Ted Lerner, there would be no going back.

“You don’t back him into a corner,” Riggleman said. “But I’m from Rockville, too.”

Before Thursday, Riggleman had twice requested to discuss his future with Rizzo, and Rizzo had told him both times he felt the time was not right. When Riggleman asked a third time Thursday, he both sealed his fate and made good on an earlier warning.

“I had told Mike, ‘I’m going to show up one day and just say, ‘I’m done,’ ” Riggleman said late Thursday afternoon. “His answer at that point was, ‘Hey, go win enough games, and we’ll talk about it.’ There’s too much of a feeling that if it doesn’t go well, that you’re going to be out of here. And that’s no way to operate. There’s got to be a little commitment from their end, some incentive from their end to go through the bad times.

“This was not a rash decision,” Riggleman added. “I love it here. I would just recommend to anybody who’s running a major franchise not to hire a coach or a manager on a one-year contract. It’s a little bit dysfunctional.”

Before the 2010 season, after he had spent the second half of 2009 as the Nationals’ interim manager, Riggleman signed a contract, in a strict legal sense, for two years with a team option for 2012 at $600,000 per season — one of the smallest managerial salaries in baseball. But the Nationals could have bought Riggleman out for $100,000 after last season.

Riggleman felt misgivings about signing the contract then, but felt he had no choice. He had not managed in 10 years, and it might be his last chance. It was the big leagues. He had grown up in Rockville. “He wanted to be there,” his son, Jon Riggleman, said. “That was the best-case scenario. You kidding me?”

When the Nationals gave Rizzo a five-year contract last fall, Riggleman assumed his situation would solidify. “Last October was the right time,” Riggleman said. “This has been festering for me since October.”

Riggleman held out hope, though, that the Nationals would start hot and Rizzo would exercise the option. As the season wore on, Riggleman realized he wouldn’t. Publicly, Rizzo backed Riggleman. But with the option year dangling, Riggleman felt a lack of confidence from ownership.

“It just didn’t have a feel that I was the person they were going to move forward with,” Riggleman said. “The first opportunity to not have me, it began to feel that that’s what was going to happen.”

Riggleman had come to feel he had to adjust his managerial style to his circumstances — he couldn’t makes decisions “outside the box,” he said, for fear of backlash if they backfired. During losing streaks, he worried if the next loss might be his last. More so, he believed managing on a one-year contract undermined his clubhouse authority.

“It’s like they’re allowed to [bad-mouth] me, and I got nothing,” Riggleman said.

And so, it had come down to Thursday. After his meeting with Rizzo, Riggleman told coaches Bo Porter and Dan Radison he would resign after the game. He never told bench coach John McLaren. After the game, McLaren said he wished he had known, so he could have tried to talk Riggleman out of it.

Riggleman managed the Nationals’ 1-0 victory over the Seattle Mariners, knowing he had chosen to make it his last game. “It was odd,” he said. He wanted to address his players one last time, but at least one team official told him he could not.

He spoke to the media in the middle of the Nationals’ clubhouse, then retreated to his office. A string of players and staff members walked in to shake his hand and say goodbye.

Jason Marquis, the starting pitcher who weeks before had squabbled publicly with him, shook Riggleman’s hand and said, “I just wanted to say thank you for everything.” Riggleman replied, “You got a new arm, man. You’re doing great.”

Soon after, a Nationals trainer came in the office.

“You shocked me,” he said.

“I’ve been thinking it over a little bit,” Riggleman said.

“I know you’ll land on your feet.”

“Who knows.”

At about 5 p.m., behind the desk in the office that was no longer his, Riggleman considered what came next. He was going to wait out the traffic before he went home. He planned on coming back Friday morning to pack his things. Friday night, he would watch the Nationals play the Chicago White Sox.

He had taken his uniform off, the crisp, white jersey that stamps you as a baseball man. He didn’t know when he might wear another one, but it had not felt strange to unbutton the last button and then pull it off.

“Nah,” he said. “If it’s the last time, it’s the last time.”