BALTIMORE, SEPT. 18 -- The Boston Red Sox can only hope their late-season fortunes do not mirror tonight's sudden collapse of Tom Bolton. But they have reason to fear otherwise, as what was left of their 6 1/2-game lead in the American League East evaporated.

Bolton no-hit the Baltimore Orioles for 6 1/3 innings, but unraveled quickly and resolutely thereafter. Cal Ripken's ice-breaking single to left field was followed one out later by four straight hits, including David Segui's three-run home run that provided a 4-1 Orioles victory before 23,308 at Memorial Stadium and left the Red Sox tied for first with the Toronto Blue Jays, who defeated the Yankees in New York.

Earlier today the Red Sox' chances in the American League East race were bolstered by Roger Clemens's successful bullpen test of his ailing right shoulder {Story, Page F9}. Tonight they were given their most forceful reminder in weeks of the downward spiral that destiny tends to always have in store for them.

Boston (81-68) lost for the fifth time in six games and 11th in 16, falling out of sole possession of first place for the first time since Aug. 19. The Red Sox, who had that 6 1/2-game lead on Sept. 4, were done in on this evening by a pair of 24-year-old rookies -- Segui and Jose Mesa, who surrendered three hits and one tainted run over seven innings.

The Red Sox are haunted by a legacy of disappointment, and they seem to be receding toward another derailed attempt to win their first World Series championship since 1918. Tonight may have been a telling stride in that direction.

Boston's postgame clubhouse was a study in trying to remain defiantly upbeat. "I don't believe in ghosts," Bolton said. "I never have. Each team determines its own fate. We won't lose this thing because other Red Sox teams lost. We'll hang in there and see what happens."

But this defeat was almost unbearably painful for Boston. Orioles rookie Leo Gomez's exciting times at third base continued, as he committed an error and was part of a misplayed popup that led to Boston's 1-0 lead in the sixth.

Bolton appeared capable of making that lead stand, but the Red Sox missed a chance to double Cal Ripken off first on Craig Worthington's liner in the seventh. Chris Hoiles and Mike Devereaux followed with singles to tie the game at 1.

Then Bolton left a 1-0 fastball high and over the plate for Segui, and the rookie first baseman sent his second major league homer -- and second in his last six at-bats -- into the left field bleachers. He had two homers in 307 at-bats for Rochester this year.

"That's what it's all about," Orioles Manager Frank Robinson said. "If you don't get a lot of hits, then bunch them."

Said Segui: "I don't think {Bolton} lost it. I don't think he pitched any differently in that inning than he did the rest of the game. The breaks just started going our way."

Mesa (2-2) and a pair of relievers made that burst of offense stand. In his fifth start since being recalled from Rochester last month, Mesa was overpowering. He reached 92 mph on one radar gun, and he was able to throw his curveball and slider for strikes consistently.

For a pitcher who has undergone two reconstructive elbow operations -- the last one just 15 months ago -- it was a remarkable show. "It's impressive for anyone," Robinson said. "What's been most impressive to me is the variety of pitches he's throwing over the plate. That says to me the arm is sound."

Mesa has allowed nine earned runs in his past 25 1/3 innings, and he has the Orioles' last two wins.

Both pitchers breezed through the early going. The Orioles' only baserunners off Bolton (9-4) in the first three innings were Worthington and Segui, both of whom walked and failed to reach second base. Baltimore managed a few well-hit balls, but outfielders Mike Greenwell and Kevin Romine each made a running catch on the warning track to take away an extra-base hit.

Mesa was undone only by the misadventures of Gomez afield. The Orioles' top prospect made two errors in his major league debut Monday, and it didn't take long for the follies to resume tonight.

Gomez made an error on Ellis Burks's fourth-inning grounder, then combined with shortstop Ripken and left fielder Dave Gallagher to pave the way for Boston's run. With one out in the sixth, Jody Reed lofted a high pop near the foul line in shallow left field.

The three Orioles converged. A popup in that area often is the shortstop's play -- "It's the play of whoever can catch it," Robinson said -- but Gomez appeared to call the others off the ball. He was standing several feet into foul territory, however, when the ball plopped on the fair side of the line while Reed pulled into second base.

After Carlos Quintana flied out, Wade Boggs made the Orioles pay with a single to right field that scored Reed. Mesa struggled through a seventh inning in which he walked two, but kept the Orioles within a run by escaping on Luis Rivera's foul popup to first baseman Segui.

Curt Schilling worked the eighth inning for Baltimore and Gregg Olson the ninth for his 32nd save.