NEW YORK -- It was a soggy Saturday morning in a nearly empty Yankee Stadium when Joba Chamberlain finally returned to a Major League mound, firing 35 pitches in an attempt to prove his readiness for prime time.

Facing live batters for the first time since his Aug. 4 right rotator cuff injury, the 22-year-old right-hander was not perfect, but he may have been good enough. Chamberlain confirmed that he is ready to be activated into the Yankees' bullpen, a decision that could come in the next few days.

After Sunday's game, Chamberlain will travel with the Yankees to Detroit, and it is possible that he could be activated as soon as Monday, when big league rosters officially expand to 40 players.

"It's kind of frustrating sitting there and seeing these guys battle and claw for nine innings," Chamberlain said. "You just sit there and you know you're not even in the bullpen or out here every five days. It'll be good to be back and in battle with these guys."

With bench players Brett Gardner and Cody Ransom recruited to take live hacks, there was a sleepy atmosphere as Chamberlain walked to the center of the diamond, pitching from behind an "L" screen.

It was 10:33 a.m. ET when Chamberlain threw his first pitch. The employees working the Yankees' public-address system got creative in playing Chamberlain's entrance song -- Motley Crue's "Shout at the Devil" -- but Chamberlain rubbed his eyes and likened the setting to an instructional league game.

He said his changeup was the best of his pitches, though he wasn't completely pleased, calling his work out of the windup "terrible" and spiking the ball at the back of the mound after his final pitch.

But watching the session from the shortstop position, Yankees manager Joe Girardi said he liked what he saw.

"When you watch a guy throw a bullpen [session], it's not 100 percent," Girardi said. "The adrenaline is not there. But he looked under control to me; he looked good to me."

Gardner tried several times to put bunts down on Chamberlain, his attempts rolling foul in each of the first six tries. Ransom took a swing and hit a sharp ground ball to shortstop, but other than that, the assorted Yankees littering the field to shag had little reason to move.

"His fastball had good life on it," Gardner said. "Obviously, it's been a little while since he's thrown on a game mound, especially against live hitters. But I thought he looked pretty good. His breaking balls looked real good."

Girardi said that the Yankees will assemble and discuss Chamberlain's next move, with general manager Brian Cashman, pitching coach Dave Eiland and head trainer Gene Monahan all to be consulted. The fact that Chamberlain bounced back well from a 45-pitch bullpen session on Thursday to throw to live hitters on Saturday is a positive sign.

"We'll wait to see how he feels tomorrow and we'll discuss the next move with him, but he said he felt good," Girardi said. "He's excited, so that's a good thing."

When Chamberlain is activated, he will return to the Yankees' bullpen, which could use the help as the club attempts to fight to remain in playoff contention.

Girardi said that he will be using his relievers in more of an October mode, evidenced by Mariano Rivera's logging more than one inning in six of his last eight outings, including a five-out save over the Blue Jays on Friday. Adding Chamberlain to that mix could help matters.

"It's another great arm on our staff, and that's what you want," Girardi said. "You want a long list of great arms on your staff, and he's another one. He gives us more depth down there and it's important this time of year."

Chamberlain opened the season as New York's eighth-inning setup man before transitioning to the rotation in June, yielding the setup role to Kyle Farnsworth, who pitched well before being dealt to the Tigers on July 30 for catcher Ivan Rodriguez.

Now, Chamberlain could be back in that original task, and he said he had no qualms about shuffling from starting to the bullpen once again.

"You have to look at it and you have to be smart about your body and tell them how it feels," Chamberlain said. "If something feels bad, you've got to be honest and tell them. We've done it the right way, and I've had support from everybody. It makes it a little easier when everybody is behind you."