The left-hander will be out to steady a rotation that has posted a 5.26 ERA over the past four games as Pittsburgh attempts to even its road series with the Colorado Rockies on Saturday night.
Locke (2-1, 3.05 ERA) has gone at least six innings while allowing three earned runs or fewer in all eight of his starts since rejoining the big league club June 8. His 2.38 ERA, 0.99 WHIP and 1.27 walks per nine innings during that time all rank among the top seven in the NL.
Locke (eight walks in nine starts) and Clayton Kershaw (14 walks in 15 starts) are the only left-handed starters with fewer walks this season than games started. His record remains less convincing largely because the Pirates have blown four leads after he's departed, though they have won six of his last seven starts.
He faced Colorado in his most recent one, surrendering three runs and seven hits in six innings of Sunday's 5-3 win, which still led to praise from manager Clint Hurdle.
"Our starting pitching got us in a position that kept us in games," Hurdle told MLB's official website after that start.
Colorado's Josh Rutledge and Michael McKenry did the damage with early home runs as Locke didn't earn a decision.
Neither did rookie Tyler Matzek, who also gave up three runs and seven hits in six innings but had a season-high eight strikeouts, and he'll oppose Locke again Saturday.
Matzek (1-4, 4.91) was called up three days after Locke but hasn't been quite as smooth. After winning his debut, the left-hander has allowed at least three earned runs in six of seven starts, all of which have resulted in team losses.
Pittsburgh (54-48) missed out on a chance to catch Atlanta for the second NL wild-card spot by losing the opener. The Rockies' 8-1 victory Friday featured a seven-run seventh and was their fourth straight home win over the Pirates.
Still, Pittsburgh has won five of seven since the All-Star break.
Colorado (42-60) has matched a season best with double-digit hit totals in four straight games while racking up 21 extra-base hits.
A strong pitching effort was more urgently needed after a 1-7 stretch with a 5.93 ERA. The bullpen still surrendered a run for the 10th straight game, over which Rockies relievers have an 8.58 ERA and .375 opponent average.
"It was nice to see our offense but it was even better to see the way we pitched tonight," Carlos Gonzalez said after connecting on his 10th home run of the season.
Gonzalez was helped along by Rutledge, who collected two hits for the fourth time in five games and drove in four runs. He's batting .417 since replacing the injured Troy Tulowitzki at shortstop last Saturday.
Pittsburgh third baseman Pedro Alvarez has been out of the lineup for two games after injuring his knee running out of the batter's box Tuesday, but he pinch hit in the seventh inning Friday and remained in the game.
Pirates second baseman Neil Walker has reached base in 22 straight games for the longest active streak in the majors.