Now he might avoid facing the man who gets on base with better frequency than anyone in baseball.
Locke (2-1, 2.89 ERA) walked 4.55 batters per nine innings last season, the biggest reason for his dreadful 6.12 second-half ERA after he made the NL All-Star team with a 2.15 ERA.
The left-hander has looked like a completely different pitcher since returning to Pittsburgh's rotation June 8. He's walked six batters in 50 2-3 innings, including none in 6 1-3 on July 11 while holding Cincinnati to one earned run before the Pirates' bullpen collapsed in a 6-5 loss.
"I'm happy about it," Locke, whose 0.96 walks per nine innings rate is fourth-best in baseball, told MLB's official website. "I'm trying to limit the walks as much as I can. Last season, it was the other way around: Limit the runs."
Locke gave up two runs - one earned - over 5 2-3 innings in Denver on Aug. 11 in his only previous start against Colorado (40-57), leaving without a decision in a 3-2 loss.
Two of his five free passes in that one were drawn by Tulowitzki, who left Saturday's game after running out a ground ball in the fourth inning. The official prognosis was a cramp in his left thigh, though considering he missed four months with a strained left groin in 2012 and two with a torn left quad tendon in 2008, Colorado figures to be extra cautious with the majors' leader in on-base percentage.
Tulowitzki himself, however, seemed relieved.
''Nothing serious,'' Tulowitzki said. ''We'll see how I wake up (Sunday). The good news is I don't think I tore anything or did anything to where I'm going to miss an extended period of time.''
Tulowitzki's counterpart at shortstop wound up giving the Pirates (51-46) their second comeback victory in as many nights. After Neil Walker's RBI single tied the score at 2 in the eighth, Jordy Mercer's double in the 11th plated Walker as Pittsburgh walked off with a 3-2 win.
The Pirates are in position to sweep Colorado for the first time ever at PNC Park, and the first time in this series since taking three in Denver in 1999.
''We feel like we're never out of anything, especially in this ballpark,'' Mercer said. ''We just kind of feed off each other and string together some good at bats, and good things happen.''
The Pirates again struggled against a left-hander Saturday, striking out eight times and getting just four hits over seven innings off Brett Anderson a night after being stymied by Jorge De La Rosa.
They'll get another look at a lefty Sunday in Tyler Matzek (1-4, 4.97), who will try to give the Rockies a third straight quality start for the first time since May 9-11.
The rookie went 0-2 with a 6.75 ERA in his final two starts prior to the break at home, though he posted a 2.92 ERA in his two most recent road starts at Milwaukee and Washington.
While Tulowitzki's status is uncertain Sunday, first baseman Justin Morneau hopes to return after missing Friday and Saturday's games with a stiff neck. Morneau, who played 31 games with Pittsburgh late last season including the playoffs, is hitting just .261 versus lefties as opposed to .332 against right-handers.