CINCINNATI — Stephen Strasburg sweated one out.

Washington’s hard-throwing rookie contained the NL’s top offense on its own turf Wednesday night, and a slumping Nationals offense finally came around behind Cristian Guzman’s homer, pulling away to an 8-5 victory over the Cincinnati Reds on a muggy evening.

A day after his 22nd birthday, Strasburg (5-2) pitched beyond his years again, passing one of his toughest tests.

“Cincinnati is first in the league in hitting,” Nationals manager Jim Riggleman said. “This is a good park to hit in. He has to be very proud of that effort.”

The Reds lead the league in batting average, hits and RBIs. They can manhandle pitchers at homer-friendly Great American Ball Park, where even a tiny mistake often ends up in the seats.

Strasburg felt he got away with a few mistakes, describing his performance as “just OK.” One of his biggest challenges was handling the humidity, which quickly left him soaked. His jersey kept coming unbuttoned after those 98 mph fastballs.

“I was trying to keep my shirt on, basically,” he said. “It was weighed down with a lot of sweat, and it kept coming open. It’s just like there were five extra pounds of sweat on it.”

It seemed like the Reds’ bats were weighed down. They had trouble locking onto Strasburg’s pitches, which varied from 81 mph to 99 mph.

“I saw a lot of good things out of him,” said Reds outfielder Jonny Gomes, who was 0 for 3 with two strikeouts against the rookie. “He throws his curve for strikes. His 100 mph (fastball) might be his third-best pitch. I don’t want to face him every day.”

Strasburg struck out seven and gave up three runs and seven hits in 5 1-3 innings, outdueling the Reds’ top pitcher.

Bronson Arroyo (10-5) had allowed only three runs in his last three starts, winning them all. Registering more typical numbers on the radar gun — 69 to 89 mph — Arroyo couldn’t keep up with Strasburg. Guzman’s two-run homer put the Nationals up 3-1 in the fifth, and Nyjer Morgan added a two-run single for a 7-1 lead.

Arroyo went 5 2-3 innings, allowing seven runs, six hits and three walks. He also struck out twice against Strasburg.

“I saw his fastball OK,” Arroyo said. “His breaking ball was big. He looked like he was throwing that 96 mph to 98 mph.”

All-Star closer Matt Capps got the last four outs in front of a capacity crowd for his 24th save.

Wherever he goes, Strasburg draws a crowd.

The Reds sold out his Cincinnati debut, the first time in four years they had a capacity crowd for a weeknight game. In 2006, they had to give away half-price tickets and $1 hot dogs to pack the house for a game against the St. Louis Cardinals.

This time, it was as easy as picking up the phone. Reds manager Dusty Baker had to function like a ticket broker for Strasburg’s appearance, getting seats for his acquaintances.

“Everybody in the world is calling for tickets,” Baker said before the game.

Even the all-time hits king showed up to get a peak. Pete Rose took in a few innings from the third row behind home plate, attending his second straight game in his hometown. This one had an unmistakable energy to it.

There was a buzz in the stands when Strasburg warmed up and started pumping 98 mph fastballs into Ivan Rodriguez’s well-padded mitt. The Reds hoped to get to him early — the rookie sometimes has problems getting going — but that plan shattered like a broken bat.

No. 2 batter Orlando Cabrera hit the ground when Strasburg threw an 81 mph breaking ball up and in. He then lined out, breaking his bat on contact.

On second glance, the Reds did a little better.

Brandon Phillips tripled to center in the third inning, and Cabrera lined a single to left on an 80 mph breaking ball for a 1-0 lead. The Reds did better at fouling off good pitches to extend at-bats — Strasburg needed 48 pitches to get through the first three innings.

By the time the Reds got to him again, the Nationals had taken control. Miguel Cairo’s two-out, two-run single in the sixth cut it to 7-3 and ended Strasburg’s outing at 97 pitches. He received a mixture of applause and boos as he left the mound.

NOTES: Riggleman said RHP Luis Atilano had a sore arm after his outing on Tuesday night, jeopardizing his next start. … Reds RHP Homer Bailey threw a simulated game without a problem. He’ll start a rehab assignment on Monday. Bailey has been on the DL since May 24 with an inflamed pitching shoulder. … The Reds expect to activate C Ramon Hernandez off the DL on Wednesday and start him at 1B, giving Joey Votto a day off. Hernandez has been on the DL since July 9 with a sore left knee. … Home run fireworks incorrectly went off after Ryan Hanigan’s fly ball went barely foul in the eighth.