In nearly two decades of professional baseball, McClain has had more than 7,000 at-bats and 362 homers. However, he'd only played in 30 major league games before Monday, when the Giants (60-79) made him one of their September call-ups. He was having a strong year at Triple-A Fresno, hitting .300 with 29 homers and 108 RBIs.

San Francisco stuck McClain in its cleanup spot on Wednesday in their series finale at Colorado. He had an immediate impact, driving in a run in the first inning and another in the third.

Then in the sixth, he did what he's done so many times in the minors - hit a long home run. His solo shot - his first ever in the majors - capped the scoring as the Giants ended their five-game losing streak with a 9-2 victory.

"All the hard work he's put in, all the home runs he's hit in the minor leagues, to get one here, the team was just elated for him," Giants manager Bruce Bochy. "It makes it all worthwhile."

The right-handed McClain, who called the homer a "moment of relief," will likely be in the lineup Friday against Pirates left-hander Zach Duke, as will some of the Giants' younger call-ups. Nate Schierholtz, a 24-year-old outfielder who's considered one of the organization's top 10 prospects, has played well twice since San Francisco called him up, going 6-for-11 with four runs scored.

Catcher Pablo Sandoval, 22, is hitting .353 since he was brought up in mid-August. he hit his second major league homer against the Rockies on Wednesday.

"They're on a mission to show they belong here," Bochy told the Giants' official Web site of his rookies. "That's what you're hoping to see out of those guys."

The Pirates (59-80) blew a five-run lead in an 8-6 loss to Cincinnati on Thursday, and on Friday they'll turn to a pitcher who is used to giving up a lot of hits. Duke (4-13, 5.14 ERA) has allowed 200 hits in 159 1-3 innings this season.

The southpaw hasn't won since June 9 - a stretch of 14 starts. Duke pitched well last Saturday, when he gave up two runs and seven hits in eight innings, but got charged with a 2-0 defeat to the Chicago Cubs.

"I feel like the work I'm doing is (headed) in the right direction," Duke told the Pirates' official Web site. "I just have to keep executing pitches."

One of Duke's four wins came against the Giants on May 6, when he yielded three runs over 7 1-3 innings of a 12-6 victory, part of a three-game sweep for Pittsburgh.

San Francisco's Kevin Correia (3-7, 5.35) didn't get charged with the loss in his last start, but he also didn't pitch well. Correia gave up six runs and seven hits over six innings in Saturday's 7-6 defeat at Cincinnati.

The Pirates have won six straight games in San Francisco and 13 of 15 against the Giants overall.