The Orioles were three outs away from moving into first place when McGwire hit an 0-2 pitch over the center field wall. The homer, his seventh, followed a leadoff single by Ruben Sierra.
A victory would have pushed the Orioles past the first-place New York Yankees, who lost to the Angels, 9-6.
"It would have been exciting to win this one today, have the crowd get into it and see Smitty shut them down 1-2-3," Baltimore Manager Johnny Oates said. "It didn't happen, but we've got a bunch of games to go."
Smith (1-2), who's headed to the All-Star Game, has only four blown saves in 33 chances.
"I wasn't trying to throw it down the middle of the plate," Smith said. "I missed my spot--and the big man didn't miss his."
Ron Darling (8-9) allowed four runs and six hits in eight innings in beating Baltimore for the first time.
Detroit 6, Texas 5--Tony Phillips tagged Tom Henke for a three-run homer with two outs in the ninth inning to rally the Tigers at Detroit in the final game between the two teams this season.
"I'm glad I don't have to see this place again," Henke said. "That's twice they got me this year on fly balls."
On May 2, Kirk Gibson hit a three-run, pinch-hit homer in the 10th inning off Henke to beat the Rangers, 10-8. But it has been a familiar scene for the Texas bullpen, which leads the major leagues with 18 blown saves--five by Henke (2-4).
Joe Boever (7-2) pitched a hitless 2 1/3 innings in relief of starter David Wells for the victory.
The Rangers, skipping batting practice for the second day in a row, tagged Wells for five runs and 10 hits in 6 2/3 innings.
Ranger reliever John Dettmer got within one out of his first major-league victory after pitching five innings of two-hit ball in relief of Texas starter Kevin Brown, who was ejected in the third. After Brown gave up a homer to Cecil Fielder, he charged plate umpire Fielding Culbreth while Fielder was circling the bases. Brown was upset over a pitch he thought was a strike before Fielder's full-count homer.
Cleveland 9, Minnesota 1--Kenny Lofton, who hit only six home runs in his first two seasons, hit his 10th in the Indians' victory at Minneapolis. The center fielder had four hits and four runs batted in.
Lofton homered off Scott Erickson (8-7) in the first inning, singled in a run in the second and doubled home two in the eighth, matching his career high for RBIs in a game.
Mark Clark (10-3) pitched despite neck pain and allowed only six hits.
Carlos Baerga, Jim Thome and Sandy Alomar Jr. also homered for the Indians, who are in first place at the break for the first time since 1959. Cleveland (51-33) has its best record at the break since 1954, when it was 56-27 and went on to win its most recent pennant.
Chicago 7, Milwaukee 2--Jack McDowell (7-7) won his fifth consecutive game and Lance Johnson drove in three runs and stole home for the White Sox at Milwaukee.
It was the White Sox's sixth consecutive victory.
Toronto 7, Kansas City 3--Juan Guzman matched a career high with nine strikeouts and Joe Carter had a homer, went three for four and drove in three runs for the Blue Jays at Toronto.
Guzman (8-9) won his second consecutive start after breaking a streak of four losses in a row. He allowed three runs on seven hits in seven innings.
Joe Hesketh (5-5) allowed five hits in seven innings.