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CHICAGO (AP) -- Enough talk about the Oakland Athletics' "Big Three." Rich Harden's ready to make it the "Four Aces."

Harden pitched seven solid innings Tuesday night to help the Oakland Athletics win their eighth straight game, a 7-2 victory over the Chicago White Sox.

"I think things are going well out there lately so I'm not taking too many chances," Harden said, who blanked Baltimore over eight innings in his last start. "I got plenty of early outs, which is important for keeping my pitch count down."

The A's matched their longest winning streak of the season and won for the 13th time in 14 games. They also extended their lead in the AL West to three games after the Boston Red Sox defeated the Anaheim Angels 10-7.

Harden (9-5) won his sixth straight decision and has not lost since a 10-3 defeat at Anaheim on June 21, a span of 13 starts.

He allowed one run on four hits and retired 11 of his last 12 batters. He struck out five and did not walk a batter.

"That fastball he's got is so free and easy and he is able to go out there and do what he wants with it because he throws so hard," said White Sox catcher Ben Davis.

Adam Melhuse went 3-for-4 with a home run and Mark Kotsay finished a home run short of the cycle despite a sore left knee.

"I'm not 100 percent, but I can help this club win some games," Kotsay said. "I wasn't hoping for a cycle but we didn't need it because we had some good pitching performances. Any injury I have I'm going to try to play through since we're heading down the stretch."

Carlos Lee hit a solo homer and drove in both runs for the White Sox, who have gone 12-24 since being 10 games over .500 on July 24 and owning a half-game lead over the Minnesota Twins in the AL Central.

Kotsay gave Harden an early lift, leading off the game with a triple off Felix Diaz and scoring on Eric Chavez's sacrifice fly for a 1-0 lead.

"Rich has really matured and is going to help us heading towards the playoffs," Kotsay said. "Pitching is going to be the focus of this team so it's our job to give them a lead to work with."

The Athletics scored three times in the second. Bobby Crosby hit an RBI double and Kotsay followed with a two-run double for a 4-0 lead.

Diaz (1-4) pitched 5 2-3 innings, allowing six runs on eight hits. He struck out five and walked two. In 26 2-3 innings as a starter, Diaz has allowed 29 earned runs.

The White Sox have spent the entire season trying to find a reliable fifth starter and White Sox manager Ozzie Guillen is having a tough time watching the auditions.

"This is 'take-five' for Felix and we got the same result, and this is like 'take-12' for the fifth starters," said Guillen. "It's hard to watch the guy you have so much confidence in before you call him up."

Oakland padded its lead in the third inning with a pair of RBI singles by Erubiel Durazo and Billy McMillon.

Melhuse homered off White Sox reliever Jon Adkins in the ninth inning.

Game notes

A's OF Jermaine Dye was not in the lineup because of a sore left thumb. He left Sunday's game in the fourth inning. ... A's C Damian Miller was a late scratch because of the flu. ... Chicago is 1-6 against Oakland this season. ... Durazo has hit safely in 16 of his last 17 games.