Cincinnati (52-67) hasn't finished with a winning record since 2000 and last reached the playoffs in 1995. Neither drought appears likely to end this year as the last-place Reds are 19 1/2 games behind the NL Central-leading Chicago Cubs.

In an effort to continue their rebuilding, the Reds traded Dunn to AL West-leading Arizona on Monday for minor league pitcher Dallas Buck and two players to be named later.

Dunn, who has spent his entire professional career with Cincinnati, is batting .233 and his 32 homers are among the most in the majors. But the 28-year-old outfielder, who is eligible for free agency at the end of the year, had gone 5-for-36 (.139) with 13 strikeouts in 10 games prior to the trade.

"It's going to be tough to replace his offense, but it's even tougher to replace the man," Reds manager Dusty Baker said.

This is the second big-name deal in 12 days for the Reds. At the July 31 non-waiver trade deadline, they sent outfielder Ken Griffey Jr. to the Chicago White Sox for reliever Nick Masset and a prospect.

Cincinnati, meanwhile, is an NL-worst 6-17 since the All-Star break and has dropped 14 of 16 overall. The Reds, who haven't lost seven straight since Sept. 22-29, wrapped up a 1-6 road trip with a 13-4 loss to Houston on Sunday. That capped a four-game sweep in which they were outscored 32-14.

Edinson Volquez (13-5, 2.93) takes the mound for Cincinnati trying to break out of a personal rut.

The All-Star right-hander has been anything but in four starts since the break, allowing 15 earned runs and 30 hits in 20 1-3 innings. On Tuesday, he gave up five runs and a season-high nine hits over five innings in an 8-1 home loss to Milwaukee.

Volquez hopes for a better outing Tuesday, though he hasn't received a decision in two career starts - both this season - versus Pittsburgh. He gave up three runs and seven hits in 5 1-3 innings of a 6-5, 11-inning home defeat on July 1.

Pittsburgh (54-64) rallied for a 7-5 victory over the New York Mets on Monday in the make-up contest of an April 28 rainout.

"It was real big for these guys to really pull together and come back," Pirates manager John Russell said, "especially 5-1 down, and didn't look like anything was going our way at all."

Jeff Karstens (2-0, 0.00) looks to continue his outstanding pitching for the Pirates.

The right-hander has tossed 15 scoreless innings in two NL starts since he was acquired from the New York Yankees on July 26 in a six-player deal for outfielder Xavier Nady and reliever Damaso Marte.

Karstens was nearly perfect on Wednesday, setting down the first 23 batters in order before Chris Young doubled with two outs in the eighth inning. He finished with a two-hitter in a 2-0 victory, walking one and striking out four.

"This is a fresh beginning, that's the way I'm looking at it," Karstens told the Pirates' official Web site. "Now I just have to keep up what I've been doing."

Karstens will make his PNC Park debut, as well as his first career appearance versus the Reds.