The Chicago White Sox were five outs away from another victory when Brett Myers reared back and hurled a fastball to Nate McLouth.
McLouth turned on the pitch and sent it soaring well over the wall in right-center. The eighth-inning drive put Baltimore ahead for one last time, and the Orioles held on for a 4-3 victory Monday night.
And so ended Chicago's six-game winning streak.
After the White Sox took a 3-2 lead in the eighth, Myers (2-2) walked Mark Reynolds with one out before serving up the ill-fated pitch to McLouth.
"I sure didn't want it to go straight over the plate, which is where it went," Myers said. "I wish I could have that one pitch back, but you know that isn't going to happen."
The White Sox got the potential tying run in scoring position in the ninth, but Jim Johnson worked out of the jam to get his 40th save.
Facing the Orioles for the first time with Chicago after tormenting them as a member of the Boston Red Sox, Kevin Youkilis hit a two-run homer in the sixth inning and singled in the eighth to set up Dunn's RBI hit. Youkilis has a lifetime .322 batting average against Baltimore, with 23 homers and 87 RBIs.
"You never want to lose a game like that. We had the lead and Nate hit that home run," Youkilis said. "We had a chance in the ninth inning to do it. It's one of those games you battle back and forth, both teams."
Baltimore improved to 24-6 in one-run games with their franchise-record 13th consecutive one-run victory.
"It was a tough one to lose," White Sox manager Robin Ventura said. "But Brett's been good to us this year."
The duel between the first-place White Sox and the surprising Orioles, who are in the midst of the AL wild-card race, attracted a meager crowd of 10,955 on a clear night at Camden Yards.
Orioles starter Wei-Yin Chen gave up two runs, one earned, and four hits in six innings. He struck out eight, including A.J. Pierzynski three times.
Down 1-0, Chicago took the lead in sixth. After Chen dropped a throw to first base for an error, Youkilis hit the next pitch into the seats in left.
Baltimore pulled even in the bottom half. A walk to Matt Wieters and a single by Lew Ford put runners at the corners with no outs and prompted Ventura to replace starter Francisco Liriano with Jesse Crain, who walked Reynolds and McLouth to force in a run. Crain then got Manny Machado to hit into a force at the plate, struck out Robert Andino and retired Nick Markakis on a slow roller to shortstop.
It was another missed opportunity for the Orioles, who had several in the early going.
In the first inning, Markakis was tagged out by Liriano while trying to score from third on a pitch that bounced away from Pierzynski and rolled to the right of the plate.
After Ford hit an opposite-field drive to right leading off the second — his first homer in the majors since July 2007 — the Orioles loaded the bases with one out before Markakis lined into a double play.
From that point, Baltimore didn't get a runner past first base until the sixth.
NOTES: White Sox RHP Gavin Floyd had a MRI on his right elbow Monday in Chicago. Ventura said no damage was found, but Floyd was scratched from Friday's start against Detroit in favor of Jake Peavy, who was slated to pitch Wednesday. Dylan Axelrod will pitch Wednesday. ... The Orioles optioned Jake Arrieta to Triple-A Norfolk to make room for LHP Joe Saunders, obtained Sunday in a trade with Arizona. Saunders will make his first start either Wednesday or Thursday, Showalter said. ... Orioles RHP Jason Hammel (knee) threw a simulated three-inning game at Camden Yards. He will next make a rehabilitation start on Sept. 1 and could rejoin the team on Sept. 6, Showalter said. ... Baltimore's Adam Jones went 0 for 4 and is homerless in 108 at-bats, tying the longest drought of his career.