Exactly five weeks after having arthroscopic surgery, Balfour pitched a scoreless sixth inning with one strikeout, no hits and no walks on Thursday.
The 35-year old right-hander needed only nine pitches -- seven fastballs and two breaking balls -- to get through the inning.
"I got one [radar gun] reading at 94, so his velocity was there too," manager Bob Melvin said. "He seemed to have some passion out there like he normally does."
Although he pitched in a Minor League game on Monday, Balfour said he welcomed the adrenaline rush of coming out of the bullpen to pitch against Major Leaguers.
"Today was really good, I was happy," Balfour said. "I had some good life on the fastball."
When Balfour had his surgery on Feb. 14, he was told the rehabilitation process would take four to six weeks. Determined not to miss any time and begin the season on the 25-man roster rather than the disabled list, Balfour worked hard and accelerated his training this spring.
"Mentally, when you tell me four to six weeks, I'm thinking the early part," Balfour said. "The season [was] in six weeks, so it had to be four. In my mind, I'm starting the season no matter what."
The Athletics expect Balfour to pitch about four more times this spring, but Melvin said that number is not concrete.
Balfour, who recorded 24 saves as the A's closer in 2012, did not pitch the ninth inning in either Monday's Minor League game or in Thursday's game.
While Melvin said Balfour may pitch the ninth in one of the final three exhibition games against San Francisco, the nine-year veteran does not feel pitching the ninth is necessary for his preparation.
"As long as I'm throwing the ninth inning when it counts, when the season starts, I'm happy," Balfour said.