However, manager Trey Hillman wasn't making any declarations after watching both pitchers on Thursday.
Bale worked five innings in a 7-2 "B" game victory over the Texas Rangers, getting six strikeouts and giving up five hits with no walks. He gave up a run on Jarrod Saltalamacchia's homer.
"Command was real good on all my pitches today, and the changeup was working real well, especially the last three innings -- it was getting some really good sink to it. Overall, I was real happy about it, except for one bad pitch," Bale said.
"He golfed it about six inches off the plate."
Pitching coach Bob McClure counted 76 pitches for Bale.
"We're looking to see if he holds his command and holds his velocity, and I didn't see him lose any of that," McClure said.
De La Rosa started the Cactus League game against the Los Angeles Angels, a 6-5 Royals win, and gave up two runs in four innings.
"De La Rosa had his best outing," Hillman said. "At times he commanded his fastball, at times he didn't. But he used the cutter more today, and when he missed with it, he threw it in non-dangerous areas. It wasn't as in command as John Bale's was this morning if you want to make a comparison of the two lefties that pitched today, but it wasn't bad."
De La Rosa also gave up a solo homer, to Erick Aybar. He walked three and wasn't happy with his command.
"I got to work on it. I threw a lot of pitches in four innings," he said. "I've got to throw less than that."
Lefty Mike Maroth made his first appearance of the spring against the Angels and gave up a leadoff homer to Terry Evans in his one inning. Right-hander Brian Lawrence, also a non-roster candidate, pitched three innings and gave up two runs.
"Both Maroth and Lawrence showed better velocity than they have been," Hillman said. "Both of them showed more arm strength according to the radar gun today, so that's a continued move in the right direction."
The last two spots in the rotation are far from settled, according to Hillman.
"As far as I'm concerned, four and five are still wide open until we see another outing by everybody," he said.
Dick Kaegel is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.