Both the Chicago White Sox and Chicago Cubs picked up surprisingly productive players before the start of the 2008 season, and they’ve been key second-half contributors to their first-place clubs.

White Sox left fielder Carlos Quentin, who was acquired from Arizona in December for minor league first baseman Christopher Carter, is the breakout stud of 2008. The 21-year-old Carter is having a terrific season at high Class-A Stockton, batting .260 with 36 home runs and 99 RBIs in 126 games, but Chicago added the major leagues’ home-run leader. Quentin has stroked 35 longballs and driven in 97 runs. In the American League, only Josh Hamilton of the Rangers (115) and Minnesota’s Justin Morneau (98) have more RBIs.

Quentin has powered a big league-high 13 second-half homers, and his .771 slugging percentage is the highest post-break mark among players with at least 50 plate appearances. A six-game hitting streak went by the boards Thursday, yet in his last seven games, Quentin is 11-for-23 (.478) with two doubles, three homers, 10 runs and seven ribbies.

The right-handed hitter is providing most of the thunder, but the White Sox are getting a big boost from Alexei Ramirez, who defected from Cuba nearly a year ago and signed with the Sox in January. He’s taken over full-time at second base, and he’s been on a 15-game surge in which he’s hit safely in 14 games. In this span, Ramirez is batting .317 with five homers and 16 RBIs.

On Aug. 17, Ramirez hit a grand slam in a 13-1 win over Oakland. It was the rookie’s second of the season, tying him for the most in the majors. Thirteen players have a pair, including teammates Joe Crede and Nick Swisher.

Ramirez has been especially effective attacking the first pitch. Among players who have put the first pitch in play 50-plus times in 2008, he is hitting a major league-high .485 (32-for-66). He’s one hit shy of .500 when jumping on the first offering.

Another key second-half contributor is Cubs center fielder Reed Johnson, who was signed by the Cubs in late March after he was released by Toronto. The right-handed hitter has clubbed left-handed pitching all season.

Since the All-Star break, among players with at least 50 plate appearances, Johnson has batted a major league-high .474 in 21 games. He trails only Quentin with a post-break slugging mark of .754.

Johnson works a successful center-field platoon with another player who was released in 2008, Jim Edmonds. As a part-time player, Johnson is 16-for-31 in August. His .516 average is the highest in the majors among players who have made at least 25 trips to the plate this month. In his last seven games, Johnson is 10-for-22 (.455) with four doubles.