CHICAGO -- Heading into back-to-back series against San Diego and Chicago, the Pirates talked about the potential to play the spoiler role down the stretch. But that task has proven to be much easier said than done.

Yes, the Pirates have their own checklist of things to play for -- pride, a sense of accomplishment and momentum for 2008 included. But as much self-motivation as can be drawn up, it can't rival the pennant races the Pirates find themselves countering.

The latest episode came Saturday, with 41,271 fans packing Wrigley Field and a Chicago team grasping a 1 1/2-game division lead.

"They're on a mission, and you can tell that they're beginning to see the finish line," Tracy said following his club's 9-5 loss. "If you're going to beat this club, you have to climb way up there to that level."

The Pirates couldn't.

The loss was the eighth straight for the Bucs, surpassing the previous season-worst skid of seven. And all of a sudden it seems as if the tables have been cruelly turned, as the contenders have spoiled the Pirates' hopes of finishing 2007 on a positive note.

"They're hungry," said Zach Duke, who made his first start since June 28. "They can taste the playoffs right now, and they're playing like a totally different team than we saw earlier in the year. They're playing like a playoff team."

And as a result, the Cubs didn't let a Pirates mistake go by without emphatically capitalizing on it. With the wind blowing in on Saturday, the four home runs by Chicago didn't rival the distance of the four hit on Friday. But the Cubs weren't concerned about style points.

In Duke's first start since being shut down with left elbow irritation, the left-hander tossed 84 pitches, three of which left the park. Those three home runs would account for all four of the earned runs Duke allowed.

"I made some mistakes, and they didn't miss them," said Duke, who entered the game with a stingy 1.42 ERA in five previous starts at the North Side ballpark. "Not good pitches that they hit really hard. That's really all it came down to."

Alfonso Soriano knocked Duke for a second-inning blast, which was sandwiched between long balls by Derrek Lee and Aramis Ramirez.

"The ball in the middle of the plate, with a club playing at the level they are, they're not going to miss those pitches," Tracy said. "[The Cubs] are performing right now at an extremely high level, and it's coming from some of the big people that they signed to do those things."

As has been the case through most of the season, Duke's nemesis proved to be baserunners. After allowing nine base hits on Saturday, Duke has now allowed 153 hits in his 100 1/3 innings pitched this season.

And Duke's four innings of work marked the seventh time in eight games that the Pirates' starter couldn't pitch past the fifth.

Regardless, getting back on the mound, doing so without pain in his arm and seeing his the movement and velocity of his pitches at the apex of where they've been all season had Duke characterizing the start as a partial success.

"Obviously I want to finish on a high note," said Duke, who dropped to 3-8 with the loss. "I want to go out there and say, 'Hey, I'm still a good pitcher.' Although the scoreboard didn't say so, I feel like I took a step in the right direction."

Tracy agreed and has Duke scheduled to make one more start before the end of the season when the team welcomes the Cardinals to town next weekend.

"I thought that the life to his pitches was better than I saw prior to him having to go on to the disabled list," the Pirates manager said. "What he is in the process of doing right now is trying to work off some of the rust."

The fourth of the quartet of Chicago home runs came after Duke's exit on a Salomon Torres' "sinker that didn't sink" to Soriano. Though he was quick to credit Soriano, who finished with a three-hit, five-RBI day, for taking advantage of a bad pitch, Torres wasn't so forgiving about the showboating he felt Soriano displayed after connecting for the two-run blast.

"I didn't appreciate the way he stood on the plate," said Torres, who was pitching after a seven-day layoff. "I wanted to say many things to him, but I said, 'You know what? Let me be professional about it.' Next time, I'll strike him out and show him up, too." From there, however, the Pirates fell hitless for the next five innings. Back-to-back extra-base hits tallied one more for the Pirates in the eighth. And Nate McLouth's solo shot into the right-field stands in the ninth plated the Bucs' final run.

But by then the sellout crowd at Wrigley was already standing and poised to sing along to the traditional "Go Cubs Go" chant after the final out.

"When you give up runs like that, there's not a whole lot you can do," Tracy said. "You can't give them opportunity because it seems like when you get the ball rolling like they have and where they're sitting right now, any opportunity you give them, they're going to capitalize."