CHICAGO -- Since Nick Johnson was traded to the Marlins on July 31, slugger Adam Dunn has become the everyday first baseman for the Nationals.

Since that day, Dunn has made one error in 23 starts at first base, but he has told interim manager Jim Riggleman and general manager Mike Rizzo there is still room for improvement.

Dunn needs improve his range going to his right. It would help if he could see the ball better when it hits the bat.

"He has improved a lot over at first base," Rizzo said. "He is still a work in progress. Although he is working out in batting practice, it's hard to take live balls off the bat."

Rizzo also said the team is going into next season with Dunn as the first baseman.

"Obviously, there are things that could change, but I do see him as our first baseman," Rizzo said.

Pitching matchup
WSH: RHP Livan Hernandez (7-8, 5.47 ERA)
The Nationals signed Hernandez to a Major League contract on Tuesday night, six days after the Mets gave the veteran his unconditional release. Hernandez will be in the rotation and serve as a mentor for Washington's young starting pitchers.

CHC: RHP Rich Harden (8-7, 4.04 ERA)
Harden was stellar in his last start. The right-hander held the Padres to one hit over seven innings, striking out eight. He has fanned 55 in 44 innings since the All-Star break and held teams to eight runs in that stretch. Although he doesn't like to acknowledge the numbers, Harden is better at night and on the road. He is 3-5 with a 6.31 ERA at Wrigley Field. He beat Washington in D.C. on July 16.

Tidbits
Right-hander Garrett Mock has won three out of his past four starts and has a 3.38 ERA in his past six starts. ... Elijah Dukes has a career-high 51 RBIs this season. ... Tuesday's victory ended a six-game losing streak against the Cubs.

Tickets
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On the Internet
 MLB.TV
 Gameday Audio
•  Gameday
•  Official game notes

On television
• MASN HD

On radio
• WFED 1500, SBN 1390 (Español)

Up next
• Thursday: Nationals (J.D. Martin, 2-3, 4.76) at Cubs (Randy Wells, 9-6, 2.84), 2:20 p.m. ET
• Friday: Nationals (John Lannan, 8-9, 4.03) at Cardinals (John Smoltz, 3-5, 7.40), 8:15 p.m. ET
• Saturday: Nationals (Craig Stammen, 4-6, 5.08) at Cardinals (Mitchell Boggs, 1-2, 4.58), 7:15 p.m. ET