WASHINGTON -- When Aaron Sanchez made his Nationals debut Saturday, the signs that he had not pitched in the Majors since Aug. 7 were there. But the signs that he could provide a lift to the rotation this season were clear, too.

Sanchez’s big league return ended up as a true mixed bag, with rocky first and fifth innings sandwiching perfect second, third and fourth innings, for a final line of 4 1/3 innings and four earned runs allowed in a 5-2 loss at Nationals Park.

At the height of his career, Sanchez proved to be an expert at inducing ground balls. In 2016, his best season, he ranked fifth in the Majors with 2.16 ground balls for every fly ball. In ‘14 and ‘15, when he was mostly a reliever, his numbers were even better. But he has battled injuries over the past four seasons and has not returned close to those marks.

Sanchez allowed three singles and a five-pitch walk within the first five batters he faced Saturday, but hidden in that sequence were hints of Sanchez’s peak form. His fastball sat at 93 mph and touched 95. And the opposing batters, while they strung together three singles, hit every ball on the ground.

• Bell exits with right hamstring tightness

After Mike Yastrzemski led off with a bunt single, Sanchez produced a ground ball for an easy double play. A walk and two singles delivered the Giants’ first run, but both hits were grounders that found holes in the infield. Sanchez made it out of the inning by picking Joc Pederson off second base.

“You got the shift and they beat the shift on a bunt, what are you going to do there?” Sanchez said. “… When I’m keeping the ball on the ground, I know that’s my game, and I’d rather get beat that way than when things start to get elevated.”

Sanchez then retired nine hitters in a row on just 30 pitches, reaching the fifth at just 47 and looking poised to go deep into the game for a team that sorely needed a lengthy start.

“What I know about Aaron, he’s a ground-ball guy,” Nationals manager Dave Martinez said. “He throws [pitches for] a lot of ground balls. When he’s good, that’s what he does. So I was pleased by that. They found some holes, but like I said, he threw the ball well.”

But Sanchez ran into trouble in the fifth. After Wilmer Flores doubled, Thairo Estrada drilled a single off Sanchez’s leg, and Luis González drove in a run with a sacrifice fly. Another single by Curt Casali ousted Sanchez after two trips through the Giants’ lineup.

Nationals catcher Riley Adams complimented Sanchez’s performance and noted that most of San Francisco’s damage came on soft contact. The Giants hit three balls harder than 100 mph off the bat -- the two consecutive singles in the first inning, and Casali’s RBI hit that ended Sanchez’s day.

While Sanchez came up Saturday because the Nationals needed an extra starter after Tuesday’s doubleheader, Martinez said afterward that he’ll pitch again when his turn comes up.

“I’ve always known this is where I belong, and I’m thankful for Washington for giving me that opportunity,” Sanchez said. “The last few years, if you look at some of my numbers on paper, some teams have written me off, and these guys gave me a chance to put a jersey back on, and not only put a jersey on but to be back in the big leagues.”

In the meantime, the Nationals lost for the fourth straight game and seventh time in their last 10, continuing to stress their pitching staff. In six games over five days, the six starters have totaled only 25 1/3 innings, leaving 28 2/3 to the bullpen. In the first two games of this series, they have used eight relievers (one twice) for 12 2/3 innings.

They'll turn Sunday to Joan Adon, who delivered the team’s best start of the week with 6 1/3 scoreless innings in the doubleheader vs. Arizona on Tuesday. Martinez said the Giants are a favorable matchup for Adon, and he also wanted to give Josiah Gray a couple of extra days of rest.

Sanchez could certainly continue to shoulder some of the load, after Martinez said “you’ll see the innings start piling up for him.”

“First time I feel like myself on a big league mound in four years,” Sanchez said, “so definitely a step in the right direction.”