PHILADELPHIA -- One pitch is all that separated Astros pitcher Justin Verlander from leaving Citizens Bank Park on Tuesday night feeling good about the way things went or second-guessing himself in the way he was ultimately forced to do in the clubhouse postgame.

Verlander, in his second start since coming off the injured list, gave up four runs in the third inning, capped by a three-run homer by Nick Castellanos that sent the Phillies to a 5-0 win over the Astros, who have lost six of their past eight games.

Castellanos homered on an 0-1 curveball with two outs -- a pitch that left Verlander wondering if he should have gone back to the fastball he used on the first pitch of the at-bat to get ahead.

“The selection bothers me,” Verlander said. “I kind of went away from my instincts there. First pitch, I just threw him a heater that my instincts said he wasn’t on, and [I] probably could have gone back to it -- and should have gone back to it -- and didn’t. That’s the game of baseball. That’s the chess match. You’ll have to ask Nick, but I felt like he was sitting soft.”

He was.

"I had a pretty good idea that I was going to see an offspeed pitch at some point in the at-bat,” Castellanos said. “And I saw that curveball pretty early, and hit it well."

Verlander gave up four runs and seven hits in five innings, walking one batter and striking out three while throwing 90 pitches. He missed more than two months with a stiff neck before returning last Wednesday against the Red Sox, when he gave up two runs in five innings (76 pitches) in a 4-1 loss to Boston.

“I felt like the first outing was a little bit better than this one,” he said. “It’s kind of to be expected a little bit. It’s kind of like Spring Training. You go out there in the first game and things feel fresh and then … not as fresh next time out. I’m fairly pleased with the pitch shapes and some of the results I’m getting.”

Verlander allowed only three singles outside of Philadelphia’s four-run third and he retired seven of the final eight batters after Castellanos’ homer. But there was no margin for error considering Phillies starter Aaron Nola dominated the Astros by throwing seven scoreless innings while not allowing a runner to reach third base.

“Sometimes you’ve just got to give credit to Nola,” Astros manager Joe Espada said. “He’s been getting out of jams for a very, very long time, and it makes him a tough pitcher. I think our approach was pretty good. We just couldn’t get some big hits. We hit some balls hard, we had him on the ropes a few times. But got to give credit, he made some pitches when he needed to.”

Verlander said getting more reps and innings will help him get into midseason form, which would come just in time for an Astros team clinging to a 3 1/2-game lead over the Mariners in the American League West. He’s thrown only 10 innings in the Major Leagues since June 9.

“I talked to a couple of buddies of mine who came back this season after being injured in the middle of the season, and I was texting them and telling them how hard it is,” he said. “In my experience, when guys are in midseason form and you’re not, it’s very difficult at this level. I think I need to take my own advice a little bit and also you don't want to become complacent. You’ve got to dial it in as fast as you can.

“When I downloaded this game, I was one pitch away from having a good outing. Even though it was a struggle -- and there wasn’t a ton of swing and miss -- I was still able to execute certain pitches in certain counts, and if I was able to make one pitch there, it could have been a completely different ballgame. That's something also I’ll focus on.”

The Astros are 2-4 on a challenging seven-game road trip through Baltimore and Philadelphia, but two of the losses were by one run and another was by two runs.

“Sometimes in these stretches, one pitch doesn’t go your way, one ball doesn’t go your way, one whatever -- it’s the difference between winning and losing,” Verlander said. “Against tough opponents, I feel like we’ve played pretty damn well. Just the wins haven’t shown up.”