If Aaron Sanchez needed any positive feedback at the beginning of his first Major League start in two years, he got some from an unlikely source: Padres third baseman Manny Machado.

In his first inning of work since Aug. 20, 2019, Sanchez unleashed a 77 mph curveball that struck out Machado, who smiled and nodded in approval as he made his way back to San Diego’s dugout.

“When you’re facing the caliber of hitter like him who’s had the success he’s had and you get a swing and miss like that, obviously that gives you confidence for the rest of the night,” Sanchez said.

Machado wasn’t the only one who came away impressed.

Sanchez displayed his intriguing upside in the Giants’ 3-1 loss to the Padres on Tuesday night at Petco Park, tossing five innings of one-run ball in his first outing since returning from right shoulder surgery.

• Box score

“You just definitely don’t know after an injury like that what the outcome holds,” Sanchez said. “You work tirelessly for a goal and you don’t really know what the outcome is going to be. To be able to walk between those lines before inning number one was super special. I felt like I was back in my element.”

The 28-year-old from Barstow, Calif., held the Padres’ deep lineup to six singles -- three of which didn’t leave the infield -- and capped his Giants debut by retiring the final seven batters he faced. Sanchez’s velocity began to dip toward the end of his 74-pitch effort, but he managed to dig deep and end his night by striking out Tommy Pham on an 89 mph fastball.

Sanchez departed with the game tied, 1-1, but the Padres went on to deliver the decisive blow on Victor Caratini’s two-run home run off right-hander Matt Wisler in the seventh inning.

Shortstop Brandon Crawford accounted for the Giants’ lone run of the night, crushing a solo shot off Padres right-hander Yu Darvish in the top of the third for his first home run of the year. It was one of three hits for the Giants, who have mustered only one run against the first two right-handed starters they’ve faced this year.

“I think we have a really good offense,” Crawford said. “I think we’re going to start getting on base here a little more and be able to drive each other in, whether it’s a home run, or an extra-base hit, or stringing some hits together. It didn’t happen tonight. I think we’re going to have some nights like this where we run into some good pitching. Darvish pitched really well.”

• Stat of the Day: Giants flying solo

San Francisco added the left-handed-hitting Tommy La Stella over the offseason in an effort to lengthen their lineup against righties, but the veteran infielder was scratched prior to Tuesday’s game with upper back tightness. Still, manager Gabe Kapler said La Stella’s back loosened up during the game, enabling him to make a pinch-hit appearance against Padres reliever Emilio Pagán in the top of the eighth.

Despite the lackluster showing from the offense, Sanchez gave the Giants another reason to be encouraged by their starting rotation, which posted a 2.93 ERA over the club’s first five games of the year. Sanchez and rotation mates Kevin Gausman, Johnny Cueto, Logan Webb and Anthony DeSclafani each made it through at least five innings, a promising sign considering the starting staff will be asked to carry a heavier workload over the course of the 162-game season.

“I think it is significant,” Kapler said. “We believe in these guys. We believed in them in camp, and we believed in them prior to Spring Training. I don’t want to come off here as surprised. We believed that they were capable of having a good first time through the rotation, and they did that.”

Sanchez was the biggest unknown in the group after missing the entire 2020 campaign while rehabbing. A one-time All-Star who led the American League with a 3.00 ERA for the Blue Jays in 2016, Sanchez landed a one-year, $4 million deal with the Giants in February after reportedly hitting 98 mph during a showcase for clubs in Miami.

After reporting to Scottsdale, Ariz., for Spring Training, Sanchez did most of his work in the more controlled environment on the backfields and appeared in only two Cactus League games before the start of the regular season. He hasn’t flashed his premium velocity thus far and averaged 91.5 mph on his two-seam fastball on Tuesday, but he said he’s confident he’ll see an uptick as he continues to build up his arm strength.

Sanchez said he had at least 15 family members in the stands at Petco Park to watch his long-awaited comeback. There were plenty of familiar faces in the opposing lineup as well, as Sanchez frequently faced off against Machado, Pham and Wil Myers while pitching for Toronto in the AL East.

The trio has seen Sanchez when he was at his best, and his first-inning exchange with Machado provided a snapshot of the form the Giants are hoping Sanchez will be able to recapture in San Francisco.

“He kind of gave me that wink like, ‘Hey, more or less, you’ve still got it,’” Sanchez said. “That was cool.”