Nick Pivetta didn’t look like a pitcher who’d been sidelined five months by a bum elbow.

Imparting fierce topspin and backspin on Monday, the 33-year-old right-hander shut out a high-powered Washington Nationals offense for five innings to set up a 3-2 victory that kept the Padres half a game out of the final playoff spot with 18 games left.

Pivetta got away with a few mistakes but displayed the basic traits that made him a top-20 starter in Major League Baseball last year and earned him the opening day slot this year.

Trusting his elbow, the Canadian broke off several snappy curveballs.

His 55th pitch on the day announced that Pivetta, should he stay healthy, can hold his own in October if the Padres can overcome the stubborn Diamondbacks to earn their fourth wild card playoff spot in five years.

The pitch nosedived straight down, a classic 12-to-6 curve that a year ago served as a staple of Pivetta’s career-best season.

Plummeting 63 inches all told, which beats the MLB average by a few inches, the pitch froze No. 5 hitter Brady House for a called third strike.

A year ago, when Pivetta posted a 2.87 ERA that landed 10th in MLB, he complemented his high-RPM curveballs with backspin fastballs that enhanced the effects of his league-average velocity.

Pivetta displayed that staple pitch, too, Monday.

The backspin played up the pitch’s average speed of 94.1 mph by creating the illusion of rise or hop.

“Fastball had a ton of carry on it,” said Nationals manager Blake Butera.

So an orthopedic surgeon wasn’t required to make this diagnosis after Pivetta walked off in the fifth inning with the Padres ahead, 3-0.

Pivetta has recovered nicely from the flexor-tendon strain suffered April 12, an injury also described generally by the Padres as an inflamed and stiff elbow.

And the pitcher seems to have cleared the mental hurdles associated with such comebacks, cutting loose with his pitches Monday.

While it remains to be seen how his arm recovers from Monday’s exertion, or whether he can build up full stamina over the three or four potential starts to come before the postseason, the performance also affirmed that Pivetta can tap into his veteran savvy.

He outfoxed several hitters on MLB’s youngest roster, changing speeds on his fastball, mixing in sliders and sweepers and throwing both his staple pitches to the top and bottom of the zone.

“He threw the ball well. I wish he didn’t throw as well as he did,” Butera said. “He was successful. He did a really good job.”

“What a performance,” said Padres manager Craig Stammen. “He exceeded our expectations. Maybe including himself also.”

Notable

Jackson Merrill helped untrack Pivetta.

The center fielder ran down Abimelec Ortiz’s first-inning rocket, completing the catch after ramming into the wall and falling to the ground.

Washington’s defenders, meantime, assisted the Padres.

James Wood lost Manny Machado’s “sun” ball in right field, leading to San Diego’s 1-0 lead on Merrill’s single.

Second baseman Jorbit Vivas’ failure to throw on time to second base contributed to San Diego adding its final two runs.

Butera said he’d “like to see a little more urgency there, (Vivas) knows that.” Of his team’s defense this season, the manager said: “In the beginning of the year, we were terrible, to put it pretty bluntly. There are still some things we need to be better at.”

A teaching moment for Luis Campusano: He was doubled off second base on Xander Bogaerts’ lineout to left field, denying the Padres a run in the eighth inning. The left-fielder’s throw got to second base before Merrill reached home after tagging up.