PITTSBURGH -- When the Pittsburgh Pirates signed Francisco Liriano this winter, they knew what they were getting.

Liriano is a 29-year-old lefty who throws hard, can deliver four pitches for strikes, and when he's healthy, racks up high strikeout totals. He is also a pitcher with six previous trips to the disabled list, a pitcher who missed all of 2007 after posting a ridiculous 2.16 E.R.A. and 144 strikeouts in 121 innings at age 22 in 2006.

Accordingly, the Pirates protected themselves in the deal, putting all kinds of incentives for health and a second year vesting option into a two-year, $12.75 million contract. And Liriano's season was delayed, thanks to a broken non-pitching arm, a malady he picked up during the holidays.

Still, what Liriano has managed to do since his first start on May 11 has been particularly remarkable. He entered Wednesday night's game against the Giants with a 1.75 E.R.A. over six starts, 11.8 strikeouts per nine innings, and just 3.5 walks per nine. He'd struck out at least seven hitters in five of the six. He's been every bit the ace the Twins once believed they had, and the Pirates had to hope they might glimpse.

Whether this form sticks around is another question. Liriano wasn't his dominant self Wednesday, allowing four runs in six innings, and striking out just two in a 12-8 win over the Giants.

But even on an off night like this one, Liriano still induced 13 ground outs over six innings thanks to his slider. Liriano is among the league leaders in throwing the slider, but he threw it even more than usual on Wednesday. After the game, reflecting on his performance in front of his locker at PNC Park, Liriano said the added emphasis on his slider was an adjustment he made based on his very first pitch.

"To be honest, I threw it first pitch of the game, and he took a swing at it," Liriano said of his initial fastball. "I just figured they were going to be looking for my fastball [most] among all my pitches. The slider was working okay tonight, but, you know, not the way I want it to."

That's a first for 2013, considering that this season, roughly one out of every four sliders he throws produces a swing and miss. That's the best mark he's posted with the pitch since 2008. Interestingly, though, he's getting even better results with his changeup, and that whiff percentage of 1-in-4 is way up from his career rates, too.

Add those two weapons, each around 86 miles per hour, to a sinking two-seam fastball that averages about 93 miles per hour, the occasional four-seam fastball, also around 93, and the building blocks for a successful starter are clear. But that's not much separation, velocity-wise. So how to account for the befuddlement of hitters this year?

"It depends on what's working that day," Pirates pitching coach Ray Searage told me, standing outside the coach's locker room at PNC Park after Wednesday's game. "I don't want to say Frankie is the quintessential left-handed sinkerball pitcher, because he's not. He will use different pitches, and throw a first pitch changeup. He'll throw a first pitch backdoor slider... It depends on the flavor the pitches are that game, and we go with them. He's an artist. He creates stuff. He does stuff that he wants to do. He's the guy who can throw any pitch in any count. When he's on, you're in for a real short night."

But ever since Liriano lost his 2007 season to Tommy John surgery, the price he's had to pay for throwing anything at anytime was walks. His walk rate was an even five per nine each of the past two seasons. A mechanical fix Searage came up with this spring has helped Liriano reduce that rate significantly, keeping him ahead of hitters, and making them particularly susceptible to swinging at those two put-away pitches, the slider and the changeup.

"All we did was get him to stay over the rubber, and make his turn over the rubber, show his back pocket to the hitter," and Searage pivoted his hips toward me, while keeping his torso facing me, to demonstrate. "Because when he does this, it just ultimately gets him back over the rubber, and gets him into his turn. So this way, it gives him enough time to get his arm up."

Liriano described the effect of this change on his pitches this way: "Trying to stay back a little longer, trying not to overthrow it every pitch. I think that's been helping me a lot."

But here's a happy accident: a mechanical change that was intended to merely improve Liriano's command has led to all of his pitches breaking more sharply than they have in years. The resulting strikeouts are almost certainly due in part to this increased movement, along with the pitcher's counts Liriano's gotten from better command. That's also allowed him to simplify, throwing his four-seamer less, and the two-seamer, which almost never produces swings and misses, as a baseline to get early-count strikes and more ground balls.

"The timing of his stride, when he comes out of that, he doesn't jump to that," Searage said of the mechanical adjustment. If he just keeps it, to his turn, it's just smooth and easy. And then the arm is able to accelerate."

So now that the Pirates have Liriano pitching the way they want him to, it is incumbent upon them to keep him pitching, period. According to Searage, the team has taken some proactive steps to keep him in one piece, in light of his injury history.

"There'll be times where I'll cancel a side [session] between two starts, just have him do flat ground, make sure they do their long-toss program. Make sure it doesn't have to be done to 250 feet. Just keeps the blood flowing, the circulation going, the muscles elongated, and know when your arm is telling you it's a little tired, to back off. And that goes also with their bodies, too. Their legs are the thing that keeps them going. So you've got to keep an eye on that, too."

Whether that will be enough to get Liriano through a full season is unclear; he's reached 30 starts just once in his career. The Pirates don't lack for starting pitching depth. But they don't have anyone like a healthy Francisco Liriano. No one does.

"I've come here, trying to learn something new," Liriano said of his recent run of success. "Learning to pitch, everything is something new. So you have to be open [to] everything. That's what I'm doing right now to get better, and it's working so far. I've gotten my confidence back, and I can go out there every night and compete, even without my best stuff."