ST. LOUIS -- Chicago Cubs manager Joe Maddon isn't fooling around. And neither are the trade-deadline additions to his club. While the fifth-year skipper integrates four new players into his clubhouse, he doesn't sound too worried about the playing-time ramifications for those already here.

"We just have to put out there what we consider to be the right thing to do," Maddon said before his team's 8-0 loss to the St. Louis Cardinals on Thursday night. "I can't be as aware, in a sense, as I was last year, in giving guys plate appearances and at-bats, developmentally speaking. We have two months to put our best foot forward. I will move guys in and out, but I don't feel as compelled to do it as I felt last year.

"It's big boy time."

That kind of rhetoric is a departure for Maddon, who always has used his entire roster and even has gone out of his way to talk up the flexibility of it. But the Cubs are in a dogfight -- entering Thursday's game, they were tied with St. Louis for first place in the National League Central -- and their struggles to separate within the division have increased the urgency. The Cubs are attempting to make the postseason for the fifth consecutive year.

"Guys that don't start can still conclude games defensively," Maddon said.

Without saying his name, that statement could be directed at Albert Almora Jr., who is a defensive whiz in center field but has struggled at the plate, posting a career-low .671 OPS this season entering Thursday. Almora was Theo Epstein's first draft pick when he took over the team in 2012, but draft status means nothing in a pennant race.

Newcomers Nicholas Castellanos and Tony Kemp figure to take playing time from Almora and others.

"To be quite blunt and honest with you, I don't care," Kemp said regarding his role. "I'm just here to help in any way possible, whether that be off the bench or if they want me to serve water to the guys. I'll do whatever they need."

That's the kind of attitude the Cubs envisioned they were getting when they acquired Kemp from Houston on Wednesday. He has been involved in big games throughout his career with the Astros, and that experience can serve him well when he steps foot into Wrigley Field for the first time.

"You take those moments, slow the game down and pretend like you're playing backyard baseball," Kemp said.

Maddon had Kemp in the lineup Thursday night, just as he did Castellanos -- the Cubs' prized acquisition at Wednesday's trade deadline. The longtime Detroit Tigers outfielder, Castellanos expressed appreciation and emotion in leaving the only MLB team he has ever known. His highest praise came for former teammate Miguel Cabrera.

"To be teammates with Miggy for six years was awesome," Castellanos said. "I was an 11-year-old kid going to Marlins Park when he debuted. Watched him bat fourth as a 20-year-old in the World Series. For me, to create a relationship with him, smile with him, compete with him, win games together and also go through extremely difficult times together, we have a good relationship."

Castellanos was told he was traded just before taking an at-bat for the Tigers as the trade deadline was about to pass. He was thrilled with the news, as was his son, who turned 6 on Thursday. It's the reason he is wearing No. 6 with his new team.

"He was excited, but he didn't know why he was excited," Castellanos said of his son, Liam. "[But] he was a little bummed, because if I didn't get traded, we had an off day in Arlington [Texas], so we were going to spend it at Six Flags. Daddy got traded. I think because everyone else was excited, he was excited."

Castellanos can make it up to his son, as there's a Six Flags amusement park just north of Chicago, but he wasn't sure when he could make it there, as his new team is in the middle of a playoff race. After years of losing baseball in Detroit, Castellanos is all-in with the Cubs.

"The two months of baseball coming up, [I'm] doing absolutely anything I can to help this squad win," he said. "I couldn't be happier where I'm at right now."

The Cubs are expecting a lot from him, as Maddon inserted Castellanos into the 2-hole in his first game, playing right field. He went 1 for 3 with a walk.

The Cubs have been searching for a leadoff hitter, so it's possible that Castellanos, who bats right, could even end up hitting first against left-handed pitching.

"I'm not a very high-maintenance kind of guy," Castellanos said. "If I have a glove and a bat, I'm ready."

Castellanos, 27, hated losing in Detroit so much, he couldn't bear to watch the playoffs. He has been to one postseason, when he was 22, and he sounds desperate for a return engagement -- which fits with Maddon's desires, as well.

"I was a bit too young to appreciate it," Castellanos said of October baseball. "I was a bit too young to appreciate the talent and the people and knowledge in that clubhouse. You don't really know what you have until it's gone.

"That baseball is unlike any other baseball."