The no-hitter was the fourth in the majors this season, joining gems pitched by the Angels' Jered Weaver, the Mets' Johan Santana and White Sox right-hander Philip Humber, who threw a perfect game at Seattle in April.
But this one was the least conventional, tying the record for most pitchers in a no-hitter.
"Those guys got all the tough outs," Millwood said. "First six, it is what it is. I've seen a lot of people do that. From seven, eight, nine — those guys got all those outs and that was special to see."
Exactly a week after Santana pitched the first no-hitter in Mets history, Millwood cruised through six innings, giving up only a walk. But after throwing his first warmup pitch for the seventh he felt a twinge in his groin and was pulled.
Seattle's bullpen never wavered, finishing the no-hitter when Tom Wilhelmsen retired Andre Ethier on a routine grounder to second base that ended a 1-2-3 ninth inning.
"That was unbelievable. I've never been a part of anything like that with that many guys coming in and keeping the no-hitter intact," said Kyle Seager, who drove in Ichiro Suzuki with a two-out single in the seventh.
The Dodgers nearly got a hit when speedy Dee Gordon led off the ninth with a slow roller to shortstop. Brendan Ryan, who had just entered as a defensive replacement, charged in and fired to first, where umpire Ted Barrett called Gordon out on a bang-bang play.
Gordon and manager Don Mattingly argued. Replays were inconclusive.
Elian Herrera then lined out to Ryan before Ethier's grounder ended the first no-hitter for the Mariners since Chris Bosio pitched one against Boston on April 22, 1993. Seattle's other no-hitter was thrown by Randy Johnson against Detroit on June 2, 1990.
"I just tried to block it out, stay within myself and execute pitches," Wilhelmsen said after earning his third save. "How tremendous was that, man?"
It was the 10th combined no-hitter in big league history and the first since six Astros accomplished the feat at Yankee Stadium on June 11, 2003. Roy Oswalt started that interleague game for Houston but left two pitches into the second inning with a strained right groin.
The 37-year-old Millwood, who spent much of last season in the minors, threw a no-hitter all his own for the Philadelphia Phillies against San Francisco on April 27, 2003.
After the final out of this one, catcher Jesus Montero ran around with his arms in the air and jumped into Wilhelmsen's arms for a somewhat-awkward celebration.
But this was no ordinary feat: The Dodgers entered with the best record in the majors and the second-highest batting average in the National League.
"This was a lot better than having it against you, that's for sure," said Seager, whose brother Corey was selected by the Dodgers in the first round of Monday's amateur draft.
Millwood came out to warm up before the seventh when the game took an odd turn. He threw one warmup pitch and stopped himself from throwing a second as he felt something wrong. Mariners manager Eric Wedge and trainer Rick Griffin came out to check on Millwood, who was replaced by Charlie Furbush.
It was later announced that Millwood had a mild right groin strain. The right-hander, who struck out six and threw 68 of Seattle's 114 pitches, said he actually felt it on the next-to-last pitch of the sixth.
Furbush retired Gordon to start the seventh, but committed a two-base throwing error on Herrera's grounder, giving the Dodgers their first scoring chance. Furbush struck out Ethier, and Wedge went to hard-throwing rookie Stephen Pryor (1-0) to face Juan Rivera.
Rivera went down on strikes but Pryor started the eighth by walking Bobby Abreu and Jerry Hairston Jr. on nine pitches. Lucas Luetge was next in line and got the first out of the inning on James Loney's sacrifice bunt.
That brought up A.J. Ellis and Seattle turned to one-time closer Brandon League, recently demoted from that role. League got Ellis to hit a sinking liner to left and defensive replacement Chone Figgins made a running catch. His strong throw home kept pinch-runner Alex Castellanos at third base.
League then struck out Tony Gwynn Jr. to end the inning.
"Really, I had visions of winning that game without a hit," Mattingly said. "First and second, I'm thinking wild pitch, sac fly. With League in the game, that split, you never know."
The previous no-hitter against the Dodgers was thrown by Atlanta's Kent Mercker on April 8, 1994. Weaver and Jose Arredondo combined to hold the Dodgers hitless for eight innings in a 1-0 Dodgers win in 2008, but that game doesn't count as a no-hitter under the rules baseball adopted in 1991 because the Angels only had to pitch eight innings.
Seattle's run came in the seventh inning thanks to a two-out rally started by Suzuki's infield single. He stole second, Dustin Ackley walked and Seager came through with his 23rd two-out RBI of the season. His line-drive single off reliever Scott Elbert (0-1) glanced off the glove of a leaping Gordon and dropped in left field.
Millwood also took a no-hitter into the sixth inning May 18 at Colorado and finished with a two-hitter. He retired his first 12 batters Friday before a leadoff walk to Rivera in the fifth.
The closest the Dodgers came to a hit off Millwood was Gordon's bunt leading off the fourth. Seager ran in from third for a fine barehanded pickup and threw out Gordon by a half-step.
"At that point of the game, it was still so early," Seager said.
NOTES: Seattle ace Felix Hernandez has been pushed back and will start Tuesday against San Diego. Hernandez has been bothered by a sore back. ... It was the Dodgers' fourth game in Seattle and first since 2000. ... It was Pryor's first major league win.