CHICAGO -- Zach Duke hardly needs touchdown-sized run support to be a winner, but that is how it is shaping up this summer.

In each of the five games he was won for the Pirates, they have scored seven runs or more.

In the other five starts, they have scored a total of five runs, including another offensive dud in the 5-2 loss to the Chicago Cubs yesterday afternoon at Wrigley Field, this despite another slick Duke line of two runs over seven innings.

Thus, all Duke's 2.75 ERA -- eighth lowest in the National League -- and remarkable consistency have reaped is a rather ordinary 5-4 record.

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Tomorrow

• Game: Pirates vs. Houston Astros, 7:05 p.m. , PNC Park

• TV, radio: FSN Pittsburgh , WPGB-FM (104.7).

• Pitching: RHP Ross Ohlendorf (5-4, 4.20) vs. RHP Brian Moehler (1-3, 8.31).

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"Look at how well he's pitched in these games where we didn't back him up, and think about what his record could be right now," outfielder Brandon Moss said. "What, like 10-0?"

Well, maybe not that high. After all, there were those three starts out of 10 where Duke had the audacity to give up more than two earned runs. And there were those two times he failed to pitch into the seventh inning.

"It's amazing what Zach's done," reliever Jesse Chavez said. "Everybody in baseball should be talking about him."

And they might be, had the Pirates not developed this trend of wasting his work in May: He opened the month with back-to-back losses in which he was charged with a total of five runs. Friday on Chicago's South Side, he pitched a complete game against the White Sox but lost, 2-0.

"These were two tough games, for sure," Duke said of these in Chicago. "But we keep battling."

"That's two games on this trip Zach should have won," Russell said. "He did another great job. Unfortunately, we couldn't hold it for him in the eighth."

Duke exited with the score tied, 2-2, and, after Chavez retired his first man in the eighth, Reed Johnson launched a 1-1 changeup into the bleachers beyond the ivy in left-center.

"He didn't get it down enough," Russell said of Chavez. "But he's been throwing very well, so, hopefully, he can just move past this one."

Chavez, whose ERA had been 1.83, had not allowed a run in his previous seven appearances, a span in which he leaned on the increasingly effective changeup.

"Not this one," Chavez said. "It didn't change much."

Chicago poured it on from there: Chavez gave up a Geovany Soto single. Sean Burnett relieved and, after an out, back-to-back RBI doubles by Andres Blanco and Jake Fox made it 5-2.

As Burnett pointed out, the bullpen has to support Duke, too.

"We try to have each others' backs here, and it hurts all of us that Zach doesn't have more wins," Burnett said.

The Cubs scored their two runs off Duke in the first inning, and they appeared plenty comfortable in the process. But Duke reversed course on falling behind and found what is becoming a familiar groove: He threw strikes, went hard to the inside and deftly mixed offspeed stuff to keep right-handed batters off-balance.

"After the first inning, I just stepped back and said, 'All right, I need to get the counts back in my favor,' " Duke recalled. "After that, I felt like I was moving the ball around very well."

He fell behind 11 of his 24 batters from the second inning onward, and he came back for a strikeout in three of those situations.

The Pirates scored once in the fourth and again in the seventh to bring the 2-2 tie: Adam LaRoche singled to open the fourth and eventually scored on Ramon Vazquez's RBI looper into left. Nyjer Morgan opened the seventh with a single off Carlos Zambrano, took third when that ball slipped under left fielder Alfonso Soriano's glove and, one out later, scored on a wild pitch.

The play at the plate, with Soto flipping to Zambrano for a tag, was close, and Zambrano engaged home plate umpire Mark Carlson with animated fury, including an apparently willful bump with the right forearm that drew an immediate ejection and likely will merit a suspension from Major League Baseball.

But that hardly was the end for Chicago's hot-headed ace: Zambrano then motioned as if ejecting Carlson, threw a ball high into the outfield, slammed his glove against the Cubs' dugout railing and took two swings of a bat into the dugout's soda dispenser before heading down the tunnel.

"I apologize to him," Zambrano said of Carlson. "After he kicked me out, I should have gone to the clubhouse and kept watching the game. I apologize to throw the ball and do other things."

The Cubs took two of three in the series, and the Pirates finished their 10-game road trip 5-5.