SEATTLE — The long road trip ended yesterday in the Northwest, but somewhere between San Diego and here, things somehow went south for the Red Sox.

In Atlanta and San Diego, the Sox continued their road mastery of National League teams, winning both series and racking up a 4-2 mark through the first six games.

But at Safeco Field, the bottom dropped out. Seattle’s 2-1, 11-inning heartbreaker yesterday capped a three-game series sweep for the Mariners, the first suffered by the Sox this season.

The setback yesterday was the eighth in a row for the Sox at Safeco, who must return here in another five weeks.

“It’s the way (the Mariners) played us,” emphasized Terry Francona, “not the ballpark.”

“Things just kind of bounced their way,” said closer Jonathan Papelbon, who stranded two runners inherited from Hideki Okajima in the ninth, then blew away the Mariners in the 10th. “Neither team deserved to lose that game.”

But the Sox did, again.

Yesterday’s loss was all the more maddening because of the circumstances. Daisuke Matsuzaka was brilliant through nine innings, checking the Mariners on one run and just three hits. His command was nearly spotless with eight strikeouts and one walk.

But once more, the Sox failed to provide offensive backing. In his last five starts, during which he’s 2-2 with one no-decision, the Sox have scored a total of five runs.

“I feel like I pitch better when it’s a tight game,” said Matsuzaka, who saw his ERA drop to 3.80, “so I can’t complain about (the lack of support).”

The one run against Matsuzaka was circumstantial. Coco Crisp, who has played almost flawless center field all season, made an aggressive play on a sinking liner by catcher Jamie Burke in the third. But the ball trickled behind him and Burke got to second with a double.

Ichiro Suzuki then flared a single into shallow center and Burke, running with two outs, scored from second.

The Mariners didn’t score again until the 11th. Reliever Joel Pineiro, a former Mariner, was thought to be unavailable thanks to a twisted ankle suffered before the game on Monday night.

After retiring Burke on a groundout, Pineiro walked Ichiro, then left a fastball up in the zone for Jose Lopez, who drilled it off the fence in left, scoring Ichiro easily with the winning run.

“I left a pitch up,” said Pineiro. “I was trying to get a ground ball. It was supposed to be down and away, but it was up and away and he got the good part of the bat on it.”

Through the first six innings, the Red Sox were held scoreless by rookie Ryan Feierbend and reliever Sean Green, though it wasn’t for lack of effort.

“Early in the game,” said Francona, “we hit balls all over the ballpark and we had nothing to show for it.”

In the seventh, the Sox finally broke through, with a single (J.D. Drew), sacrifice, a Mariners’ error (on Julio Lugo) and a sacrifice fly (by Crisp).

But too often, the Sox batting order sputtered.

David Ortiz was 0-for-5. He flied to left with two on and two out in the third, grounded to second with the bases loaded in the fifth, flied to right with a runner on first in the seventh and fanned to end the ninth. Four of his five at-bats ended Red Sox innings.

Cleanup hitter Manny Ramirez was no more productive, going hitless in five at-bats, though thanks to Ortiz, he led off in four of those at-bats.

The Sox put the leadoff man on base in the eighth and 11th, but stalled both times.

In the eighth, with Youkilis (walk, passed ball) on second and two out, the Mariners elected to intentionally walk J.D. Drew to get to slumping Lugo, who has gone longer than Elvis without a hit.

Francona had lefty Eric Hinske on the bench, but the Mariners had southpaw Ryan Rowland-Smith warming and didn’t want a poor matchup. Predictably, Lugo struck out, running his hitless streak to 30 consecutive at-bats.

As a team, the Sox were 0-for-8 with runners in scoring position and stranded 11 baserunners.

“We hit some balls well today,” said catcher Jason Varitek. “But we just didn’t get it together offensively.”

In the first two nights, the Sox wasted 11 runs in the two losses. When they could have used some of that sock yesterday, it was nowhere to be found, sending the Sox home with a losing record on the trip, a condition they couldn’t have imagined Sunday night as they left San Diego.

smcadam@projo.com