BALTIMORE, SEPT. 19 -- Pennant races have a way of locating the cruelest avenues to defeat for the Boston Red Sox. Such was the case again tonight, as former Boston phenom-turned-spare-part Sam Horn blasted a three-run home run to put the Baltimore Orioles on their way to an 8-4 victory over the suddenly second-place Red Sox before 25,598 at Memorial Stadium.

One-time Boston farmhands Curt Schilling and Brady Anderson also played parts in the Red Sox loss, but Horn had the leading role in ejecting them from atop the American League East for the first time since July 30. Boston, which has lost six of its last seven and 12 of 17 games, fell one game behind the victorious Toronto Blue Jays.

The Red Sox (81-69) led the division by 6 1/2 games 15 days ago. Their derailing now seems nearly complete, as they battled internal unrest this afternoon and allowed the sixth-place Orioles (67-81) tonight to finish capturing their first series against AL East opponents in 14 attempts.

The Red Sox were beaten here for two straight nights by pitchers who had two prior big league wins, and today they yielded Baltimore's largest offensive explosion since a nine-run day at Fenway Park 26 games ago.

"We have to get ourselves together or this won't even be a race in too long," said outfielder Mike Greenwell, whose three hits included a solo homer. "We can't allow ourselves to give up here. We can still get this thing together, even if it doesn't seem like it right now."

In an evening full of Boston mistakes, perhaps the most glaring was made by Manager Joe Morgan -- who allowed tiring starter Greg Harris to face Horn with one out and two runners aboard in the fifth inning.

Horn is batting .340 with 17 RBI in his past 14 games, and he already had hit the ball hard off Harris in his first two at-bats of the evening. He carries something of a grudge against his former employers, whose regular lineup he never cracked before signing with the Orioles last winter as a minor league free agent.

Horn tried to hide that bitterness tonight, but it slipped through when he was asked about delivering a heavy blow to Boston's AL East chances. "All I can say about that is that I hope so," he said. "If they have players who they feel can do the job that I did when I was there, then good for them.

"I'm just happy to be in baseball and happy to be with the Orioles. When I came over here, they made me feel like I was an important part of the team. . . . It's going to stick in their minds that Sam Horn hurt their chances, especially if they keep sliding the way they are."

Joe Hesketh was warming in the bullpen before the homer, and Horn likely would not have been allowed to face the left-hander. But Morgan let Harris remain, and Horn picked on a high fastball to send his 13th home run of the season -- in his 218th at-bat -- into the right field bleachers.

Morgan said he never considered removing Harris, and Harris took the blame after the game with a stinging self-critique -- and a backhand swipe at Horn.

"I was just a stupid idiot today," Harris said. "To let Sam Horn beat me in a game that means as much as this is ridiculous. I let everybody down. I didn't do what I was supposed to do.

"It will take a while to live this one down. No way I should be beaten by this man. That's a guy I wanted to pitch to, who's never touched me." Horn was one for 10 against Harris before the home run.

The blow broke a 2-2 tie and made the 100-pitch, five-inning struggles of Baltimore starter Anthony Telford (3-2) worthwhile. Schilling, traded with Anderson for Mike Boddicker two years ago, registered his third save with four innings of one-run relief.

The Red Sox already had begun to feel the strain of their faltering bid to win the division; they're not wearing their tensions well. After they lost to the Orioles here Tuesday on rookie David Segui's seventh-inning home run -- and the Blue Jays tied them for first -- catcher Tony Pena conducted a showy postgame tantrum that included throwing a chair across the clubhouse and yelling that his teammates were "a bunch of quitters."

The Red Sox tried to present an all-is-well stance today, but the sentiment seemed forced. Greenwell said Pena owed his teammates an apology, to which Pena agreed and added that he meant only that some Boston players had quit on some games, not on the season.

But the Red Sox' fall threatens to tie the largest Sept. 1 lead ever blown by a first-place team since divisional play began in 1969 -- 6 1/2 games, a mark held by the '78 Red Sox. Boston's advantage is that it plays eight of its final 12 games at home; the Blue Jays finish with a nine-game road trip.

The Red Sox grabbed the early lead tonight, getting a run off Telford -- who has lasted only 18 innings over his last four starts -- on singles by Jody Reed and Carlos Quintana and Wade Boggs's sacrifice fly.

The Orioles managed two runs in the second for a 2-1 advantage. Catcher Chris Hoiles led off with the first of his three hits -- a double to left-center field. Bill Ripken scored him by fighting off Harris's two-strike curveball to dump a single into right, then went to third on Anderson's single one out later and came home when a Harris fastball in the dirt got past Pena for a wild pitch.

Boston tied the contest at 2 in the fourth but probably should have done better. Pena's RBI single scored Greenwell, but Luis Rivera's bid for a three-run homer down the left field line hooked just foul. Asked to assess Telford's efforts, Morgan said: "Just fair. . . . He got lucky, let's put it that way."

Following Horn's heroics, Greenwell's solo homer brought Boston to within 5-3 in the sixth. But the Orioles -- aided by Boggs's throwing error -- managed two runs off three Red Sox relievers in the bottom of the inning for a 7-3 cushion.

"It's satisfying any time you can knock a team into second," Schilling said. "But it's better that it's Boston."

Orioles Notes: Shortstop Cal Ripken had three hits to extend his hitting streak to 12 games, best on the team this season. . . .

Club officials will begin three days of organizational meetings at a local hotel Thursday. The annual sessions are aimed more at evaluating talent than making specific decisions about the maneuvers the team will try to make in the offseason, General Manager Roland Hemond said. . . .

Pitcher Brian DuBois today underwent what Orioles officials termed successful surgery on his left elbow. A tendon from his right foot was implanted in his elbow.