Palmeiro, 40, has 566 home runs, ninth on the all-time list.
As he stood on second base, his teammates, coaches and sons Patrick and Preston came running onto the field to congratulate him. Fighting off tears, Palmeiro grabbed 10-year-old Preston and lifted him in the air. The crowd gave him a standing ovation for three minutes.
After the game, Palmeiro was welcomed back to the clubhouse for a champagne toast by manager Lee Mazzilli. In fact, a bottle of Domaine Michelle champagne sat in each player's locker.
"I was numb going around the bases, and for the most part I don't remember anything," he said. "I guess I am glad it's over with and now we can concentrate on the season," he said to the media afterward, his uniform sprinkled with champagne. "It was emotional. I wasn't expecting (the ovation). I really appreciated that."
Palmeiro entered this season with 2,928 hits, and he made a push toward 3,000 in the past month, when he emerged as a force in the Orioles' offense. He collected 25 hits in June and also drove in 20 runs. He entered Friday's game 7-for-30 in July after collecting a fourth-inning single off Aaron Sele on Thursday for No. 2,999.
The Safeco Field crowd gave Palmeiro a standing ovation, and Seattle fans have seen him on base plenty of times over the years. His 227 hits against Seattle pitching are his second-most against any team, and his 51 home runs are the most of any opposing player against the Mariners.
Palmeiro is in his second stint with the Orioles, having played for the team from 1994 to 1998. He signed a one-year contract to return to Baltimore in 2004, and signed another contract for 2005, realizing that he could reach 3,000 in a Baltimore uniform.
And he found the moment breathtaking.
"I really couldn't hear anything," Palmeiro said. "This has to be up there. Not many people can get to 3,000 hits. I would have to say this is one of the most important moments of my career. Right now I just want to enjoy the moment and maybe I will reflect later on."
Of his 3,000 hits, 544 have been collected at Camden Yards, his most in any ballpark. And he has maintained that he wants to go into the Hall of Fame with an Orioles cap.
But it's been a long, arduous road for Palmeiro to reach this pinnacle. He was a first-round pick of the Chicago Cubs in 1985 and collected his first Major League hit on Sept. 8, 1986, against Philadelphia's Tom Hume. A day later, Palmeiro hit his first Major League home run off Kevin Gross.
Cubs officials felt that Palmeiro would be nothing more than a spray hitter, and they dealt him to Texas in an eight-player deal that also brought Jamie Moyer to the Rangers.
It was in Texas that Palmeiro flourished, developing power in addition to his ability to hit for average. He collected his lone 200-hit season with the Rangers, compiling 203 in 1991, and on May 20, 1993, he reached hit No. 1,000 against Chicago's Alex Fernandez. Palmeiro established himself as a model of consistency, collecting at least 38 home runs and 110 RBIs for nine consecutive years, starting with Baltimore in 1995.
Palmeiro left the Rangers for the Orioles the year before, signing a five-year contract with Baltimore and emerging as one of the game's elite hitters. He collected hit No. 1,500 on May 20, 1996 against Anaheim pitcher (and current Oriole) Jason Grimsley, and Palmeiro helped the Orioles to consecutive playoff appearances in 1996 and '97.
After some tough negotiations with the Orioles at the conclusion of the 1998 season, Palmeiro returned to Texas on a five-year contract, where he reached several milestones that many Orioles fans wished he could have accomplished in Baltimore.
He reached hit No. 2,000 on May 2, 1999 against Cleveland's Rich DeLucia, and then No. 2,500 on April 16, 2002, a double off Anaheim's Al Levine.
All the while, Palmeiro was rapidly approaching 500 home runs, and he became the 19th player to reach that milestone with a shot off Cleveland's David Elder on May 11, 2002, at The Ballpark in Arlington. Much to his chagrin, the reserved Palmeiro was lavished with adulation after the feat.
"I've never played this game for the fanfare or the attention," he said. "I've played this game because I loved this game from the very first time I ever played it when I was 9 years old. That's all I ever wanted to be."
And three years later, he is hearing the cheers again, this time for one of the game's great accomplishments. But the humble Palmeiro still downplayed his achievements.
"You are talking about the two best players of all time," he said of Mays and Aaron. "I am in a group with them but that doesn't mean I belong with them. Hank Aaron has 200 more than I do and Willie Mays has 100 more. They are in a class by themselves."