The two teams meet Monday in the first game of a three-game series at Wrigley Field with rosters that are radically different from when they opened the season.
The Astros, who sit in last place in he NL Central with a 38-78 record, 31 1/2 games behind the first-place Reds after Sunday's 5-3 loss to the Brewers, have parted ways with a number of veterans -- including third baseman Chris Johnson, pitchers Wandy Rodriguez, Brett Myers, Brandon Lyon and J.A. Happ, and first baseman Carlos Lee.
In their place have come a steady stream of organizational prospects and young players acquired in trades, and a few experienced veterans looking to re-establish themselves in the Majors.
One of those is 30-year-old right-hander Armando Galarraga, he of the near-perfect game but for a controversial umpire call while with the Tigers in 2010.
Galarraga, who will be making his fourth start for the the Astros on Monday, is 0-2 with a 4.70 ERA and has battled control problems.
In his last outing Wednesday vs. the Nationals, Galarraga walked six and gave up six hits in five innings, but he persevered to give up just three runs in a 4-3 loss.
He's walked a total of 13 batters in his last three starts.
"I threw the ball bad," he said after his last start. "I'll be honest with myself. Six walks ... there's not an excuse for that. I need to make adjustments and work on my mechanics."
Astros manager Brad Mills likes what he has seen of Galarraga, but acknowledges the need for improvement.
"He's got good stuff, but we'd like him to pitch on the plate a little bit and kind of work ahead of hitters," Mills said after Galarraga's last outing. "It gives the pitchers a lot of confidence, and I think that's one of the things that got him in trouble today."
The Cubs are in fifth place in the NL Central with a 44-69 record after Sunday's 3-0 loss to the Reds, 24 games out of first place.
They, too, have undergone a heavy roster makeover, including trading starting pitchers Ryan Dempster and Paul Maholm. With right-hander Matt Garza on the disabled list, 27-year-old right-hander Jeff Samardzija finds himself as the most experienced member of the starting rotation.
Samardzija, who will be the Cubs' starter Monday, is 7-10 with a 4.21 ERA in 23 starts in his first full season in the rotation.
Samardzija was good in his last outing on Wednesday, pitching seven innings of four-hit ball and giving up one run, but he took the loss in a 2-0 defeat at the hands of the Padres.
Samardzija let his frustrations show, breaking his bat over his leg after striking out in the seventh inning.
"It just felt good to snap it like a toothpick," he said.
"When you start losing games and a lot of things aren't going your way, you're going to see some frustrations come out," Cubs manager Dale Sveum said. "That's part of the game. It's OK to see guys with emotion and fire. Those are guys you want around, too."
Samardzija was appreciative of Sveum's leaving him in to work his way out of difficulty in his last inning.
"Any time you're a young guy and your manager lets you pitch around a hit and pitch around a walk, and you see those pitches up in the 100 count, those are times you want to prove to your manager you can pitch and have your stuff," Samardzija said. "I felt great there with my pitch count what it was. You take more pride when they leave you out there, and you want them to remember that you pitched well for the future."
It's all part of the learning process, Sveum said.
"In that situation, it was his game," Sveum said. "He had pitched a great game. You're hoping for a double play, and he has a chance for a win. We just couldn't get anything going."
Astros: Green, Pearce help out
Tyler Green started at second base on Sunday and went 2-for-5 after playing shortstop in Saturday's game and going 2-for-5.
The Astros got Green on Thursday in a trade with the Cardinals.
Steve Pearce started at first base Sunday and went 1-for-4 after going 3-for-4 with three RBIs on Saturday.
The hit extended Pearce's hitting streak to eight games and upped his batting average to .368 since being claimed on waivers two weeks ago.
Cubs: Vitters to get starts
Rookie third baseman Josh Vitters, the Cubs' No. 3 overall pick in the 2007 First-Year Player Draft, will get at least two starts in the series with the Astros, Sveum said.
"He'll probably play maybe all three games against Houston, and we'll kind of see after that," Sveum said.
Vitters will get a lot playing time the rest of the season, Sveum said.
"That's going to be the evaluation in the next 50 games, however many he plays, the exposure," Sveum said. "This is a lot of evaluation, and we'll see where we're at as soon as he's getting more exposed with game-time ground balls and everything."
Despite Sunday's loss to the Brewers, the Astros still came away with a series win, just their second road series win of the season. The last one came June 8-10 against White Sox.
The Cubs have lost three straight and 11 of their last 12 games.