The Baltimore Orioles built a 4-0 lead today for left-hander Scott McGregor, who had won five in a row and had a career record of 11-1 against Detroit. Game over, right? Wrong.

Baltimore Manager Earl Weaver's expression and words showed how wrong, as he tried afterward to explain how McGregor gave up nine hits, six for extra bases; why Lenin Sakata was called upon to pinch hit with a resulting double play, and how Doug DeCinces wound up in left field for the first time in his major league career.

Weaver had an answer for everything, except why the Orioles cannot win on Sunday. With the bottom third of the batting order scoring all their runs, the Tigers rallied for a 5-4 victory on Lynn Jones' two-run double in the sixth, reducing Baltimore's lead over second-place Milwaukee to two games. The Orioles, 27-8 the rest of the week, stand 1-8 on Sunday.

McGregor had retired 13 of the first 15 Tigers when the bottom third of the lineup unloaded in the fifth. Tom Brookens grounded a double just inside third base. Then Stan Papi, a .250 hitter forced into designated-hitter status by injuries, sent his first home run of the season into the left field bleachers and suddenly it was 4-2.

Journeyman Mick Kelleher followed with an opposite-field double to right and came across when Alan Trammell dropped a two-out blooper into right center. That was the Tiger's sixth hit, but first single.

The same crew chased McGregor in the sixth. Papi opened with a ground single between short and third. Then, with most of the folks in the ball park expecting a bunt, Detroit Manager Sparky Anderson instead ordered a hit-and-run, with No. 9 man Kelleher at bat.

Shortstop Mark Belanger broke toward second, then stood helplessly as Kelleher sent what would normally have been a routine double-play grounder through his vacated position. Jones followed with his double to the base of the left field wall, scoring both runners and completing the day's run production.

"I was mad at myself because I anticipated," Belanger said. "But I waited as long as I could. The pitch was on the way, so I finally broke. I just wish I'd waited a little bit longer."

"You won't ever get a better chance to put something on," Anderson said. "The situation was tailor-made. That kid (Kelleher) can handle the bat and I knew McGregor would be throwing strikes. All McGregor is hoping is to get that out. Of course, if he pops it up . . ."

"We lost because they didn't bunt and we didn't try nothing," Weaver said. "You've got the No. 9 man and you let him swing away and he executes. That's the way to play baseball. If he swings through or takes the pitch or anything else, you're a lousy manager. But he executes and you look good. That's when a manager puts his job on the line."

Right-hander Aurelio Lopez (2-1), who relieved rookie southpaw George Cappuzzello in the second inning, struck out seven Orioles between the fourth and seventh innings and was the winning pitcher.

With one out in the seventh, singles by Eddie Murray and Jose Morales prompted Anderson to call in lefty Kevin Saucier, who had yielded only one run in his last 11 appearances.

Weaver sent Sakata up to bat for John Lowenstein. Sakata promptly grounded into a rally-killing double play.

"Sakata was four for five pinch hitting with a homer, and John ain't seen five left-handers in two years," Weaver said. "When you're a player short, it hurts. You're short one piece of the puzzle."

The Orioles were short Al Bumbry, who pulled a muscle in his left thigh on Friday. So Gary Roenicke played center, with Benny Ayala in left, and when Baltimore jumped ahead, 3-0, and Detroit switched to a right-hander, Lowenstein replaced Ayala. That created a dearth of outfielders and, after Sakata's failure in the pinch, DeCinces moved to left for the last two innings, catching the only ball that went his way.

Saucier retired three straight in the eighth, then walked Roenicke to open the ninth. Rich Dauer sacrificed, but Ken Singleton grounded to second and Murray broke his bat on a ball that wound up in second baseman Lou Whitaker's glove to end it.

Saucier, the expatriate from the world champion Phillies, cavorted like a crazy man in joyous celebration of his fifth save and said later, "So I'm a looney. There's nothing wrong with that. I'm having a good time."

The Orioles' good times were confined to ruining the 27-year-old Cappuzzello's major league debut -- with Murray's two-run homer inflicting the principal damage -- and to counting the house. The crowd of 28,011 boosted attendance to 522,764 in 23 dates, the earliest jump over the half-million mark in the team's history.