Gio Gonzalez allowed no runs and four hits as he pitched into the ninth inning for the first time since 2013. (David Kohl/USA Today Sports)

The Washington Nationals began the season’s second half Friday much like they spent the previous six weeks: dealing with a dose of dispiriting injury news, this time on Joe Ross’s elbow and Jayson Werth’s big toe. They were just the latest developments in a season that has been stretching the first-place club’s depth thin in every department. “We’re the walking injured,” Manager Dusty Baker declared.

But the top three in Washington’s starting rotation, perhaps the best threesome in baseball, remains intact, and the Nationals chugged along to another victory Friday, downing the Cincinnati Reds, 5-0, at Great American Ball Park with just four regulars in their lineup behind 8⅓ scoreless innings from Gio Gonzalez.

“That was as sharp as I’ve seen him,” Baker said, “and the longest.”

For all the depletion, the Nationals (53-36) still boasted a dangerous middle-of-the-order Friday, even without Daniel Murphy, who was given the day off after spending most of his break in Miami for the all-star festivities. Fellow all-star Bryce Harper picked up some of the slack, smashing two home runs in the first five innings off Reds right-hander — and Georgetown product — Tim Adleman, who lasted all of 4⅓ innings.

“Man, we have depth and we’re not afraid to use it,” Baker said. “Whoever we put out there, we think they’re going to do the job.”

All-star snub Anthony Rendon did his part, too, going 2 for 3 with a walk, a double and an RBI. He complemented his work at the plate with his usual dazzling defense at third base.

“Defense was definitely working for me,” Gonzalez said. “Rendon made, I couldn’t even keep count. . . . Of the top 10, he’s probably going to make six of the highlights.”

It was all in support of Gonzalez, and it was plenty. Gonzalez, who made his own all-star case without a nod, continued his standout campaign with his best start in nearly two years. The left-hander pitched into the ninth for the first time since Sept. 9, 2013. He held Cincinnati to four hits. Three were of the infield variety, and the Reds (39-50) hit just four balls to the outfield at the bandbox of a ballpark. Gonzalez, who retired 11 straight batters at one point, struck out six and walked two. His ERA stands at 2.66. Two qualified National League pitchers have a better mark. Their names? Max Scherzer and Clayton Kershaw.

“I was just trying to keep the ball down and follow Matty’s idea,” Gonzalez said. “Matt Wieters, he had the game plan that he wanted, and we stuck by it, and I just followed his lead.”

The Nationals usually convene for an on-field workout in Washington the Thursday during the all-star break every season. It is essentially a rare practice session, an opportunity to get the gears going again before the grind restarts.

This year, however, the Nationals had to push the workout back to Friday afternoon because Nationals Park was occupied Thursday in preparation for a James Taylor concert Friday. So they ventured onto the field at Great American Ball Park at the height of a scorcher at 2:30 p.m. Infielders took groundballs. Outfielders pursued flyballs. Pitchers ran.

They all greeted each other as if they hadn’t seen other in months because a four-day hiatus does seem like a months-long interruption in the baseball sphere. Then they began batting practice just after 3 p.m. — nearly three hours before the road team usually takes its hacks.

The unusual itinerary didn’t preclude the Nationals from pouncing on Adleman. Brian Goodwin, moonlighting for the injured Michael A. Taylor in center field, smacked the game’s second pitch for a double. Consecutive two-out RBI singles from Stephen Drew, starting at second in place of Murphy, and Rendon later in the inning put Washington up 2-0.

Two innings later, Wilmer Difo, starting at shortstop in place of the injured Trea Turner, led off with a single, and Harper followed with the first of his homers. The blast went 111.7 mph off the bat. In the fifth inning, Harper launched a leadoff home run 440 feet to the batter’s eye beyond the center field wall. The ball bounced off the grassy knoll to center fielder Billy Hamilton, who kicked it up into his glove with his right foot. The hacky sack trick was probably the Reds’ most impressive play of the night.

“Just trying to get in the swing of things again,” Harper said. “Try to get a pitch out over the plate that I could drive, and I got two tonight.”

That concluded the evening’s scoring, though the shutout nearly didn’t survive two outs from the Nationals’ bullpen. Gonzalez, to his surprise, was sent out for the ninth inning with his pitch count at 109 to face Joey Votto, one of baseball’s premier sluggers. He got the left-handed-hitting Votto to fly out on the fourth pitch, which prompted Baker to emerge to replace him with Matt Albers with Adam Duvall, a right-hander, due up.

Duvall and Eugenio Suarez welcomed him with consecutive singles before he could get an out. After Scott Schebler struck out, Jose Peraza reached on an infield single to load the bases and chase Albers. Matt Grace, a lefty, was called on to face Tucker Barnhart, a right-handed hitter. He needed just one pitch to induce a groundball that Drew snatched with a dive to his left for the elusive third out. It was Grace’s first career save and preserved Gonzalez’s work on a day that began with more bad news and ended with another victory.