BALTIMORE - A pitching duel between an up-and-coming lefty and a veteran right-hander was decided by a utility player in the role of emergency starter.

Luke French took a one-hitter into the eighth inning, Matt Tuiasosopo homered and had a career-high four RBIs, and the Seattle Mariners beat Kevin Millwood and the Baltimore Orioles 4-0 on Tuesday night.

Tuiasosopo had an RBI double in the fifth and hit a three-run homer in the ninth. He learned 20 minutes before the game that he would start in place of Ryan Langerhans, who was a late scratch with a severe headache.

"I just wanted to go out there, and ... find a way offensively or defensively to help this team win a game. Just be loose and have fun," Tuiasosopo said. "Gosh, it feels really good."

Tuiasosopo came into the game with a .155 batting average, one homer and two RBIs in 71 at-bats.

"Playing here and there only a few times a week is tough," he said.

Seattle interim manager Daren Brown, now 5-3 since taking over for Don Wakamatsu, said of Tuiasosopo: "It's good to see him when he gets an opportunity like he did tonight. He's got a chance to be a good offensive player."

French (2-3) allowed two walks and no hits over the first five innings. The left-hander got the first out of the sixth before rookie Josh Bell bounced a single to left.

Losing the no-hitter wasn't a big issue, especially in such a tight game.

"If you start worrying about that, you might start getting in trouble," he said.

French retired the first two batters in the eighth before Bell doubled and Brian Roberts got an infield single. Brandon League then retired Nick Markakis on a grounder.

League worked the ninth, earning his third save.

French has bounced back and forth between Seattle and Triple-A Tacoma this season, but if the left-hander continues to pitch like this, he has a chance to stick for good.

"I don't have any control over that," French said. "I just have control over how I prepare and how I work and being ready every day. Anytime you get to play up here it's a big opportunity and a lot of fun, but as far as worrying about that kind of stuff, I just try to tune that out."

Millwood (2-13) gave up one run and six hits over eight innings in one of his best outings of the season. But he was betrayed by a lack of run support, a common occurrence during the worst season of his 13-year big league career.

"I expect Kevin to pitch well," said manager Buck Showalter, 10-5 since his debut on Aug. 3. "He gives us a chance to win. He did it again tonight. We just didn't do much with French."

Millwood has been backed by only 87 runs in his 24 starts, and the Orioles have scored just 51 runs while he's been in the game. That goes a long way toward explaining why he's 0-5 in eight starts since June 24.

The only run Millwood allowed came in the fifth, when Adam Moore led off with a single and scored on Tuiasosopo's double.

But that was enough to saddle him with another loss.

"I worry about things I can control, and scoring runs is obviously not something I can control," Millwood said. "I feel like if I go out and pitch well, give us a chance, then I've done my job."

In the ninth, Armando Gabino gave up a single and a walk before Tuiasosopo homered to left.