Joe Crede also connected for the White Sox, who made up deficits of 4-2 and 6-4 in handing the Orioles their 12th loss in 14 games. The defeat dropped Baltimore (51-52) under .500 for the first time since April 9.
Pierzynski, whose previous career high was 11, began the year with 37 homers in 1,899 career at-bats. Asked to explain his sudden power surge, the catcher replied, "No idea. I wish I knew. I'm just getting balls up in the right spot. I'm hitting a lot of balls
with more backspin. I used to hit a lot with more tailspin."
In that situation, he'd have happily settled for a single.
"I was just trying to hit a fly ball and not hit into a double play," he said.
Four pitches later Dye hit his 21st, the seventh time this season the White Sox have homered in consecutive at-bats.
Iguchi capped his second straight three-hit game with an RBI single in the ninth.
"We're a scrappy team," Chicago manager Ozzie Guillen said. "The home runs, that's a plus. The one thing with the home runs is when you have people on base, we can make a lot of things happen."
Rafael Palmeiro gave Baltimore a 6-4 lead in the sixth, hitting his 18th home run with a man on. It was his 1,191st extra-base hit, moving him out of a tie with Lou Gehrig into sole possession of sixth place on the career list.
On July 15, Palmeiro become the fourth player in major-league history to have 3,000 hits and 500 homers. He now has 3,017 hits and 569 home runs.
Brian Roberts drove in two runs for Baltimore. Left fielder Eric Byrnes, who flew overnight from Colorado after being traded from the Rockies for outfielder Larry Bigbie, went 1-for-5 with an RBI in his Orioles debut.
But it all went for naught, and a team that in was first place and 14 games over .500 now has a losing record. Manager Lee Mazzilli insists Baltimore is still a playoff contender.
"Absolutely, no question," he said. "What are we going to do, fold the tent up? You can't do that. I'm not going to let that happen. You've got 60 games left, and you've got to make the most of it."
Javy Lopez, who went 1-for-4, said, "One game can change it around. That's the game we're waiting for."
Baltimore starter Daniel Cabrera left the game in the second inning after being struck on the back of his pitching hand by a line drive off Crede's bat. X-rays on the right-hander were negative, and the injury was determined to be a bruise.
"It's fine," said Cabrera, wearing a wrap to minimize the swelling. "I think I'll be all right for the next start."
It was the second time in three games that a Baltimore starter was forced out after being hit by a line drive. Sidney Ponson
bruised his right thumb Thursday night in the third inning against Texas.
Down 2-0, the Orioles took the lead against Jose Contreras with a four-run third. Two singles and a walk loaded the bases for Roberts, who hit a two-run double. Another run scored on a wild pitch before Byrnes grounded an RBI double inside third base. The uprising was blunted, however, when Contreras picked Byrnes off second.
Chicago got even in the fifth inning against Bruce Chen, making his first relief appearance of the season. Chen, who gave up three homers in four innings against Texas on Wednesday, yielded a leadoff home run to Crede. Juan Uribe then doubled and scored on a single by Iguchi.
Chen yielded two runs and four hits in 1 1/3 innings.
After Dye hit an RBI single in the second, Chicago made it 2-0 against Jason Grimsley in the third. Iguchi got a triple when Jay Gibbons failed to make a diving catch on his liner to right, and Carl Everett followed with a sacrifice fly.
Contreras gave up six runs in six innings. ... Palmeiro's two RBI gave him 1,834, moving him past Dave Winfield into 14th place on the career list. ... Chicago improved to 13-6 against the AL East and lifted the majors' best road record to 34-16. ... Iguchi has four of Chicago's eight triples this season.