It marked the first time Lackey has faced hitters since undergoing Tommy John surgery last offseason.
"It's the first step in the new world for him after a real hard summer of rehab," Valentine said. "Better than how he looked, is how he felt. He said he felt great afterwards, and that's important.
"He looked OK, considering it was his fist time. His breaking ball was really good, which is usually the last thing, and he's been working on that less. It was good. He just didn't have real good control of his two-seamer."
If his arm feels good Sunday and he continues to progress, Lackey likely would throw another live session Wednesday.
"It was kind of weird being on a game mound, man; it's been a while," Lackey said. "The arm feels good, but the location's not where I want it to be, obviously, but at this point, I just want the arm to feel good and I'll worry about the other stuff later on."
"He looked really good," Lester said.
Valentine said Friday there was a possibility Lackey could make an appearance in a big-league game in some capacity -- maybe just an inning or two -- before the end of the season, but Lackey dismissed that notion.
"I'm not going to pitch here," he said. "No, I'm not going to push it that hard. My doctor doesn't want me to pitch this year. (My arm) was pretty messed up, so he wants it to rest."
There is, however, a chance that Lackey could throw in the Arizona Fall League if he wants to see some game action before spring training.
Lackey has drawn criticism since arriving in Boston, especially last season when he posted a 12-12 record and a 6.41 ERA. Even before he signed a five-year deal worth $82.5 million as a free agent, the club already knew the right-hander had a bad elbow and would need surgery at some point.
Lackey pitched all of last season with severe discomfort. But now that he's closer to returning to game action, Lackey's thrilled with that thought.
"Man, it's the light at the end of the tunnel," Lackey said. "It's been 10 months of a grind, really. I've been doing a lot of exercises every day, trying to get back right, and it's nice to get a little treat like that to throw off a mound."
Valentine is impressed with the work Lackey has put in to return to this point.
"From the first day of spring training, when I saw John in the weight room, I was impressed with his work," Valentine said. "He's missed one day all year. It's been really impressive."
That one day, as Valentine explained, was due to a "move" he had to make at his home in California.
With the 2012 season quickly coming to an end, Lackey should be ready for spring training and possibly could return to the rotation early next season.
"It's hard to tell," Valentine said. "I would think, though, that he would be really close.
"If he continues to work hard all winter, which I believe he will, he'll give us and himself the best chance. Now, whether or not it has to be Opening Day, I can tell you right now I don't think that's necessarily the goal. To get him back healthy is the key -- 100 percent."