I don't try to come up with a story from a Kershaw vs Petit match-up. The Nats were pretty well handled by Kershaw (as expected). I wouldn't go as far to say the Nats were dominated, but I'd also don't think Kershaw had his A+ stuff either. On the Nats side Petit did pretty much what you wanted him to do, go 6 and hold it close. The bullpen let in another run. This time it was Perez, who they tried to work into just getting out lefties, but Chase Utley got a big single to add an insurance run. Solis looked good but how much of that was a 3 run lead in the top of the 9th with Jansen coming in and it being 96 degrees I don't know.
So with nothing much to say about that I wanted to talk about Gio for a second. I've heard some "what's wrong with Gio" talk. I've heard some Biogenesis whispers. This is all silly. There is a very simple explanation for Gio's decline. He's getting older.
When Gio came to the Nats the big worry was that he'd give up a lot of homers. That had been an issue early in his career and on the road as an Athletic. Since DC wasn't as pitcher friendly as Oakland it seemed that it might be an issue here, but that didn't happen. He adjusted. Not only did he not give up a lot of homers, he reigned in his control, too. In 2012 he paired that with being harder to hit, which gave us the Cy Young contender year, but even after with more typical "hittability", he kept those other things going and gave the Nats two solid years.
This makes sense in hindsight. He had a few years under his belt and was still improving. He was entering the window most people think of as peak, 26-28 years old. He was going from the AL to the NL, always a nice bonus for pitchers. Everything was lined up for him.
Now he is exiting his peak. He can't keep it up. What's being effected now is his hittability. The hits per nine are going way up the past two years. He countered that by becoming an extreme ground ball pitcher last year, which kept his home runs down. But it's hard to keep the ball down, yet close enough to the strike zone to not walk a lot of guys and induce strikeouts. Gio saw his walks bump way up and his K's go down. He saw his IP per game go down to 5.6. He was doing ok, but not great and he wasn't lasting long enough.
So he adjusted again. He's been putting move balls in the zone this year. His IP per start is back closer to 6 now. The walks are down but the flyballs go up. His stuff is just in general more hittable so the homers go up a lot too. He plugs one hole in the dam here, another one opens up over there.
Gio was a great strikeout pitcher (9th in K% for qualifying pitchers* from 2012-2014), with iffy control (16th worst in walks), who was hard to hit (4th in BAA - better than Stras or ZNN, even taking out 2012 he only drops to 12th). He could concentrate on keeping the ball in the park to make himself a top pitcher.
Gio IS a very good strikeout pitcher (26th 2015-16) with iffy control (13th worst), who is no longer hard to hit (20th worst). Simply keeping the ball in the park no longer works to make himself a top pitcher. He now has to pick his poison. He can keep the ball in the park, but give up more hits (BA goes up with GBs as opposed to fly balls) and probably more walks and less Ks too. Or he can worry about keeping the walks and Ks where he likes, probably control the hits a little bit, but give up more homers.
This is who Gio is now. A pitcher with flaws that can't be hidden or worked around. It doesn't mean he can't be an effective pitcher. He can be. Hell he'd probably be a 3 on most teams. But hoping for anything better than what you are seeing in general, for any long stretch, is probably asking too much.
*131 from 2012-2014, 74 from 2015-2016 if you must know. It does inform.