"It's a tough time to play us," said A's manager Art Howe. "We're playing playoff-type ball right now. Everything is working for us. Appier went right at the hitters. It was just a clinic out there, and we're swinging the bats as well as we have all season. It's fun to come out here and play."
Appier (11-9) won his second decision in as many starts with the A's, who improved to 8-1 on the homestand.
Jim Parque (9-8) allowed six runs, seven hits and two walks in four innings. He did not strike out a batter for the first time all season. Parque has not won in seven starts dating to July 7.
"I felt lost out there," Parque said. "I kept making bad pitch after bad pitch. I got the wind knocked out of me early and never got it back."
After Jason Giambi's RBI single in the first, which extended his hitting streak to 15 games, gave the Athletics a 1-0 lead, Oakland scored five times in the fourth off Parque.
Miguel Tejada hit a two-run double and Grieve hit a three-run shot over the right-field fence for his 17th homer.
Thomas homered with one out in the sixth to become the 84th player in major league history to reach 300 home runs. The homer snapped also an 0-for-10 streak in the series.
"Maybe this will help me get my swing back," said Thomas.
Thomas also becomes the fifth active player to record at least 300 homers, 1,000 RBI (1,031) and 1,000 walks (1,050). He joins San Francisco's Barry Bonds, Tampa Bay's Fred McGriff, St. Louis' Mark McGwire and Baltimore's Cal Ripken, Jr.
"This was really big for him and the team," White Sox manager Jerry Manuel said. "He's been depressed that he couldn't get it sooner. It's an important milestone for Frank and hopefully the team will respond."
The A's scored three more runs in the seventh on a bases-loaded walk to Grieve and A.J. Hinch's two-run single. Oakland added two in the eighth when Randy Velarde tripled and scored on Giambi's groundout and an RBI double by Scott Spiezio.
Giambi went 3-for-5 and is now hitting .459 (28-for-61) with 24 RBI over his last 15 games.
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