CHICAGO -- Chris Coghlan continues to prove why he's a good fit in the third slot of the Chicago Cubs' batting order.

Powered by Coghlan's two home runs and four RBIs on Friday at U.S. Cellular Field, the Cubs won their eighth straight game with a 6-5 victory to start a series against the cross-town rival Chicago White Sox.

The Cubs have won 14 of their last 15 games and are now 12-0 when Coghlan hits third.

"I thought we was swinging the bat well, and I kind of liked it because he's an on-base (percentage) guy," Cubs manager Joe Maddon said of his reasoning for placing Coghlan there in the order. "He's probably had the worst luck of any of our hitters all season, hitting the ball hard and having it turn into an out."

Maddon also said he considers the third spot, ahead of power hitters Anthony Rizzo and Kris Bryant, to be a prime place to use a pinch-hitter from the other side of the plate in the late innings.

Either way, the strategy is working out well thus far for the Cubs, who haven't had a streak of this length since winning nine straight games in 2008.

Coghlan hit a three-run homer in the third inning to give his team a 4-2 lead and then hit the first of back-to-back solo homers in the fifth, which put the Cubs ahead 6-5 and wound up being the final margin.

The result evened the season series at two wins apiece, with games left Saturday and Sunday to finish this year's installment of the rivalry.

Former Cubs starter Jeff Samardzija had another rough outing for the White Sox, who had a three-game winning streak snapped.

Along with Coghlan, the Cubs got a homer from Rizzo (1-for-3) and 5 2/3 scoreless innings from their bullpen. Four relievers combined to shut the White Sox down after taking over for starter Kyle Hendricks with one out in the fourth.

Left-hander Clayton Richard picked up the win after throwing two innings, right-hander Justin Grimm struck out three in 1 2/3 innings, right-hander Pedro Strop stranded the tying run on second with back-to-back strikeouts in the eighth and right-hander Hector Rondon pitched the ninth for his 20th save of the season.

"Clayton was huge in today's game," Maddon said. "We hit the home runs, we had some good at bats ... but when Clayton did come in, he really did define the game at that point, permitted (Grimm) to Strop to Rondon with the lead. And that was really important to have the lead because they have an outstanding bullpen themselves."

Proving that point were White Sox left-hander Zach Duke and right-hander Zach Putnam, who combined for three scoreless innings after Samardzija left the game.

"I think at that point it was tough to see and guys where throwing hard and just really shut it down," White Sox manager Robin Ventura said. "I think both bullpens have been doing that as of late."

Center fielder Adam Eaton went 2-for-4 with a two-run homer and right fielder Avisail Garcia went 1-for-5 with a two-run double to lead the White Sox.

Samardzija had a third straight poor outing and has now allowed at least four earned runs in five of his past six starts. He fell behind 1-0 in the first, gave up a 2-1 lead on Coghlan's three-run shot in the third and coughed up a 5-4 lead on the back-to-back homers in the fifth.

"I feel great, I feel like my pitches are there," Samardzija said. "It’s just a couple swings of the bat here and there that are getting me, and in big situations. We need to keep doing what we're doing, keep improving, and we'll be fine."

NOTES: The White Sox activated UTL Emilio Bonifacio (oblique strain) from the 15-day disabled list and optioned UTL Leury Garcia to Triple-A Charlotte. ... The White Sox announced that OF Micker Adolfo, 18, has undergone season-ending surgery to repair a fractured fibula. Adolfo, a highly rated prospect signed in July 2013, was injured sliding into a base during an Arizona League game. He's expected to fully recover by spring training next year. ... Cubs manager Joe Maddon said RHP Rafael Soriano, who's on the 15-day DL with right shoulder inflammation, is close to starting a minor league rehab assignment. ... The White Sox honored legendary former SS Minnie Minoso and pitcher Billy Pierce by wearing throwback uniforms from the 1950s. All White Sox players and coaches wore Minoso's No. 9 for the game. Minoso died March 1 at age 90. Pierce died July 31 at age 88. The Cubs wore their 1950s-era road uniforms.