The Astros, who finished April with a 9-19 record, were shut out for the third time this season after going 1-for-8 with runners in scoring position and stranding 10 on base. They also committed two errors which led to runs.
"We couldn't mount any offense, couldn't come up with the big hit," Porter said. "At the same time, when a guy shuts you out, he threw the ball pretty good."
Nationals starter Jordan Zimmermann (2-1) held the Astros scoreless for 6 1/3 innings, allowing seven hits, one walk and striking out seven batters. It was his 45th career victory, making him the winningest pitcher in Nationals history (2005-present).
"My first inning, I threw 20-something pitches and basically the whole game, I was trying to battle back to get the pitch count manageable," he said. "They fouled some good pitches off and made me work."
Astros starter Brett Oberholtzer (0-5) has lost five of his six starts this year, but only recently has begun to struggle. He threw 4 2/3 innings and allowed a career-high 11 hits and a career-high-tying six earned runs while striking out five. In his last two outings, he's given up 19 hits and 12 earned runs in 8 1/3 innings.
"I think when you look at his last couple of outings, and I talked to [pitching coach Brent Strom] about it, it looks like he's gotten away from pitching on the inner third of the plate," Porter said. "When you get predictable and it's one side of the plate, Major League hitters are going to take advantage of that. He left some balls up.
"You look at the success he had last year, it was the ability he had to use both sides of the plate, the ability to use his secondary stuff."
The Nats took a 1-0 lead in the third when Denard Span hit a ball into the gap in right-center field for what looked like a sure triple. Astros rookie right fielder George Springer struggled to pick up the ball on the warning track, and Span circled the bases for a triple and an error on Springer, who's already made five errors in the outfield.
"I think a lot of it is speed of the game," Porter said. "It's not physical, like he doesn't have the physical tools to make these plays. I think, one, there has to be a maturation that takes place. You look at the play today -- it's a double or a possible triple. It's a speed guy who hits the ball in the gap. From an outfield standpoint, there is nothing you can do to prevent him from getting to second base for sure. Now, if you hit the relay man and it's a great relay and everything goes right and he's out at third on the slide, then good job. But do your part, pick up the ball and hit the cutoff man."
Washington scored four times in the fourth to take a 5-0 lead, pushing across the first run of the inning on a missed catch by first baseman Jesus Guzman. Rendon had a two-run double to left later in the inning, and he scored on a Jayson Werth single.
"The errors that concern me are the impact errors that lead to runs, like both of the errors we had today," Porter said. "Those are the type of errors you want to stay away from."
Oberholtzer said the Astros haven't come out ready to win at times.
"We're not going to beat anyone on a day-to-day basis with our talent," he said. "But we definitely have to do a better job of willing ourselves to compete on a day-to-day basis and matching the intensity the other teams bring to the game."
Considering the Astros are 2-14 when the opponent scores first, Oberholtzer has a point.
"We need to come out and try to jump on some teams early," catcher Jason Castro said. "That's when I feel like we have our most success is when we're able to get on the teams early and try to continue that throughout the game."
Castro, who went 0-for-3 with three strikeouts, said he didn't think preparation was an issue.
"I can't speak for everybody," he said. "I can only speak for myself. I'm definitely fully prepared before every game. From what I've seen, I think guys are going out there with a solid game plan and have an idea of what they're going to do."
Three of the hits the Astros managed against Zimmermann were infield hits, including back-to-back singles by Springer and Guzman in the fourth. The Astros managed only one extra-base hit among their nine hits, while the Nationals had six.