PHOENIX -- Judging by the impressive manner in which Jose Contreras threw off the mound on Monday morning and how confidently he spoke about his first Spring Training bullpen session a few hours later, the right-hander appears to be well on his way to breaking camp with the team.

Going purely by the sound of Bartolo Colon's pitches smacking the mitt of catchers Jared Price and Logan Johnson, the burly right-hander also might be ready for the start of the 2009 season. Colon, who's recovering from the removal of bone chips in his right elbow, was thought to be a bit behind Contreras, who is battling his way back from a ruptured left Achilles, but Colon appeared to turn it up a notch Monday with hitters actually in the batter's box.

"It's incredible the way Bartolo threw today," said Contreras through translator and Minor League coach Rafael Santana. "His breaking ball, he had good command. I think Bartolo is almost ready.

"I was very much impressed the way Bartolo located his pitches, and he was throwing hard. It was popping."

Colon and Contreras each threw 40 pitches, divided into two 20-pitch "innings," with Minor Leaguers such as Matthew Inouye and Miguel Negron taking hacks. Contreras used all of his pitches, from all of his angles, just as he had done in three previous side sessions off the mound.

The repertoire for Colon basically was limited to fastballs and changeups, again similar to his three side sessions last week. But Colon also broke off a few sharp curves on Monday, fooling the Minor League hitters.

Once Colon gets his arm strength up to regular-season readiness, there certainly are no worries about Colon's skill and craftiness.

"Bartolo has tremendous pitchability. He's got really good movement, and he can change speeds," said White Sox pitching coach Don Cooper, who watched Colon on Monday while manager Ozzie Guillen followed action at a B game on a nearby field. "Everything went good today for him. The feeling I'm getting, and he's saying it a little bit, 'I've got more. I've got more.' But we don't need more right now.

"More ain't better, and where he's at is fine. We're going to continue to progress from here. Both of them threw a real good amount of strikes, and now we're starting to judge them more not only on how they feel, before, during and after, but now it's not going to be long before they face hitters. We're starting to look at their location."

Cooper originally spoke of another bullpen session set for Wednesday involving Colon and Contreras. But Contreras left camp on Monday to return home to Florida, where he officially will become a U.S. citizen on Wednesday in Tampa. Contreras returns to Arizona on Thursday, when he and Colon figure to throw that second bullpen.

Contreras said he was told by athletic trainer Herm Schneider that he will be pitching to "a couple of people" in Saturday's game at home against Texas. But nothing is guaranteed in regard to this duo's return, with their health status really being a day-to-day proposition.

Still, the White Sox certainly are excited by the possibility of having Colon and Contreras fill out the rotation.

"That's very encouraging. I heard they have been throwing well," starter Mark Buehrle said. "That's going to be a key to our success -- having those guys in there and healthy."

"Obviously, it makes us deeper," said John Danks, who worked two innings during Monday's loss to Cleveland. "We have the young guys that are capable of getting outs, and then to throw in some veterans like that, it does nothing but help."