Prior gave up one run on four hits and two walks while striking out three over four innings Thursday against the San Diego Padres in a rain-shortened game. All of the hits came in the first inning.
The next step for Prior will be the Cubs' game March 28 against the Colorado Rockies. Carlos Zambrano was originally scheduled to start that game, but he will throw in the Minor League camp.
"This turn around the rotation will be the most important for our pitchers," Cubs manager Lou Piniella said Friday. "We look for our pitchers to throw about 100 pitches this juncture, starting with Zambrano today, then [Ted] Lilly, [Jason] Marquis and [Rich] Hill. The last time out, we'll shorten everybody up to 60, 65 pitches so they're fresh for the season."
The Cubs need to see Prior in a Cactus League game rather than have him throw in the Minors.
"I think it's more important for Prior to pitch under these circumstances than sending him down to the Minor League club," Piniella said. "Obviously, it's more competitive, and there's going to be more scrutiny to perform."
Prior's fastball was clocked between 86-87 mph on Thursday, and he did touch 89 mph.
"[Thursday] was an improvement, obviously, and everybody was pleased," Piniella said. "Today was very positive. He had normal soreness that a pitcher has, normal stiffness, and nothing more."
After the outing, Prior said he would be ready when the Cubs need a fifth starter on April 7. Piniella didn't want to look that far ahead. He was encouraged that Prior was able to work some changeups in Thursday's outing.
"The first 16 breaking balls he threw this spring were all balls," Piniella said. "The other day, he got quite a few over. His mechanics are starting to feel better to him and they're producing more strikes.
"He looked nice and comfortable and confident on the mound," Piniella said. "That's just one time. Let's see what happens here the next time. One thing that we've done with Mark, and I think it's really helped him, is that we haven't set any timetable, we haven't rushed him, we've given him all the time and it's working. Why all of a sudden go into rush mode and risk a setback? Let's see what happens next week."
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.