Just one night ago here in Memorial Stadium, the Baltimore Orioles made a mockery of themselves with five errors, plus four other buffooneries worse than many a miscue.

Now, just one night later, the Orioles, playing with the defensive precision and grace of nine Mark Belangers, not only beat the California Angels, 4-3, but moved into first place in the American League East by half a game.

Actually, it was one Belanger who played like nine tonight. Belanger, back at shortstop despite lingering back pains after a four-game absence, had 10 flawless chances to support Dennis Martinez's seven-hitter and Rick Dempsey's two-run game-winning home run off loser Goeff Zahn in the fifth inning.

The Orioles, winners of five of their last six, could hardly have atoned with more style. Martinez (10-4), who is tied with Ken Forsch for most victories in the league, struck out five of the first eight Angels, including the side in the first. Then he summoned extra-adrenline speed when, after two singles with two out in the ninth, he struck out pinch hitter John Harris to finish with a whoop. Martinez pulled the same game-ending strikeout trick on Harris June 7 in Anaheim.

The Orioles could have wilted after their new nemesis, ex-mate Bobby Grich, put them behind with a three-run opposite-field homer into the Angel bullpen with two out in the fourth inning. That blow was particularly dispiriting because Martinez, after retiring 11 of the first 12 Angels, suddenly threw eight consecutive balls before Grich stepped up. After those two walks, Martinez hummed a good, low fast ball that Grich demolished for his 10th poststrike homer.

The Orioles responded immediately as Al Bumbry beat out a chop to open the fourth, then scored on Rich Dauer's double to left center. A bloop hit by Ken Singleton moved Dauer to third, whence he scored on Eddie Murray's grounder to cut the deficit to 3-2.

Both Bumbry's and Singleton's hits might have been outs on superior plays. Again in the fifth, the absence of Angel gloves helped the Orioles. Butch Hobson kicked Gary Roenicke's leadoff grounder, then Roenicke rode home as Dempsey hit a "fast ball down the middle" into the Oriole bullpen for the game-winner.

When was Dempsey's last game-winning homer?

"Three years ago," he said with a grin.