That could mean bad news for the Miami Marlins, who have won three of four despite inconsistent run production.
The Pittsburgh Pirates hope for Locke's fourth win in five starts Friday night when they visit the Marlins.
Locke (9-2, 2.11 ERA) experienced soreness in his back during a 2-1 loss against Oakland on July 8, then missed his next scheduled start and was held out of the All-Star Game. But he looked no worse for wear Sunday, allowing an infield single, four walks and one run over six innings of a 3-2 win at Cincinnati.
It marked the left-hander's fifth quality start in his last six games, and his ERA crept closer to Clayton Kershaw's major league-leading mark of 2.01.
"The back's great," Locke told the team's official website. "Just going back to last week, pretty much proved to myself today that I stand by the decision that was made by the club and myself (to not pitch July 14). It's more important to miss one start to feel healthy and hopefully feel good the rest of the season."
Pittsburgh (60-40) had its four-game win streak snapped Thursday by Bryce Harper's walkoff home run in a 9-7 loss at Washington. Meanwhile, Miami (38-62) comes into a 10-game homestand after taking three of four in Colorado despite totaling 13 runs and 17 in its past eight games.
Giancarlo Stanton had two doubles in Thursday's 5-3 victory after going 2 for 21 in six contests since the All-Star break.
Long-term offensive improvement could be even harder to come by for the Marlins after learning Thursday they would be without rookie outfielder Marcell Ozuna for the rest of the season because of a left thumb injury. The team's leader with 24 extra-base hits, Ozuna suffered torn ligaments and an avulsion fracture while making a diving catch in Monday's game against the Rockies.
"He did a great job," manager Mike Redmond said. "He makes a game-saving catch, gets hurt, and ends up on the DL. It's really unfortunate."
Henderson Alvarez (0-1, 3.28) will hope for better support than he received in his previous start. He turned in his best performance in four outings for the Marlins, throwing seven shutout innings of five-hit ball in a 1-0 loss at Milwaukee on Sunday.
"I felt like I was locked in from the first pitch," said the right-hander, who also recorded his first career hit.
Miami's Placido Polanco is hitting .256 - his lowest mark since his rookie year of 1998 - but is 29 for 85 (.341) against left-handers.
Starling Marte is 1 for 24 through his last six contests after going hitless in three at-bats Thursday, though he walked twice.
The Marlins had won 14 of 16 in the series prior to the Pirates taking four of five last year despite being outhit, 46-33. Andrew McCutchen was 7 for 17.