In order to make room for Mazzaro, the club optioned infielder Steve Tolleson to Sacramento, from which he was recalled on April 27. He made his Major League debut the following day and singled Friday in Toronto for his first big league hit.
Mazzaro, meanwhile, was 1-1 with a 2.59 ERA in five games -- four of them starts -- with the River Cats. The 23-year-old did not allow a run in three of his five outings and began the season with a 12 1/3 inning scoreless streak.
The young pitcher is no stranger to Oakland, though. Mazzaro made his Major League debut with the A's last June and went 4-9 with a 5.32 ERA in 17 starts before being shut down in September with right shoulder tendinitis.
The A's are hoping they witness the Mazzaro that lit up as a June callup, the one who didn't allow an earned run while winning his first two starts. He proved to be far less effective after the All-Star break, going 2-4 with a 7.21 ERA. Furthermore, the club is counting on a lower WHIP, which stood at 1.74 upon his exit last year.
"He feels good," manager Bob Geren said. "He feels confident, and he's been throwing the ball well."
In five games (two starts) with the A's this spring, Mazzaro was 1-0 with a 6.28 ERA. He surrendered 15 hits and eight walks through 14 1/3 innings while building up his arm strength.
"He's back in the strike zone, his stuff is back and his velocity is back," Geren said. "We're looking forward to seeing him."