Locke struck out six and allowed four hits over 5 2/3 innings in his International League debut as Indianapolis fell in Louisville, 4-1. The left-hander hasn't allowed a run in his last two starts, an 11 2/3-inning span.
The Pirates' No. 8 prospect threw 88 pitches and did not walk a batter after going 7-8 with a 4.03 ERA in 23 outings at Double-A Altoona.
The Braves' second-rounder from 2006, Locke joined the Pirates organization in '09 and split the past two seasons primarily at Double-A. A similar performance on Aug. 10 -- 5 2/3 scoreless frames against New Britain -- was the latest in a line of recent quality starts that prompted the Bucs to promote the 23-year-old.
All four hits the Bats managed against Locke came with two outs. He struck out two and worked around a single in the first before retiring 12 straight batters between the first and fifth innings. A pair of singles put a runner in scoring position with two outs in the fifth, but Locke whiffed opposing starter Tom Cochran.
He set down the first two batters of the sixth before Juan Francisco's single to right field prompted the Indians to call on Jared Hughes to finish the frame -- Hughes caught Denis Phipps looking to protect Indianapolis' 1-0 lead.
Locke also looked good at the plate with a two-out single in the third in his first Triple-A at-bat. He was 2-for-18 at the plate with Altoona, with both hits coming on May 11.
Locke's chances for a win ended in the eighth when the Bats rallied for four runs off Daniel Moskos, the Bucs' top pick in 2006. Francisco lined an RBI single and Moskos (1-1) issued consecutive walks to load the bases before stepping aside for Justin Thomas, who hit Dan Dorn to force home a run. Mike Costanzo added a sacrifice fly in the frame.
Locke and the Indians lost manager Dean Treanor after the first inning after he argued with home plate umpire Craig Barron and first base umpire Fran Burke before being ejected.
A native of North Conway, N.H., Locke began the year behind Rudy Owens as Pittsburgh's No. 2 left-handed prospect. A Florida State League All-Star last year with Class A Advanced Bradenton, Locke also earned All-Star honors last month in the Eastern League. Drafted out of high school, Locke was also an All-Star in 2007 with Rookie-level Danville, when he went 7-1 with a 2.66 ERA in 13 outings for the Braves.