SAN DIEGO -- It didn’t take Kyle Harrison long to flash his electric stuff when he debuted with the Giants last year, but he left some room for improvement when it came to efficiency.

The 22-year-old left-hander completed six innings only once in his seven Major League starts last season, but he managed to match that mark in his first appearance of the 2024 campaign.

Harrison struck out five over six strong innings to lead the Giants to an 8-3 win over the Padres on Friday night at Petco Park, giving the club its first victory under new manager Bob Melvin.

Third baseman Matt Chapman crushed two home runs -- his first pair for the Giants -- and added an RBI double to back Harrison, who allowed only solo shots to Manny Machado and Fernando Tatis Jr. and walked none in the economical 76-pitch effort.

Fifty-five of those offerings (72%) were fastballs, which topped out at 95.8 mph and generated each of Harrison’s five punchouts.

“Fastball felt really good,” said Harrison, the Giants’ No. 1 prospect. “The plan for me today was to really just get ahead of guys and attack them as much as I can and limit the walks. It ended up being that way with the fastball. I loved establishing that early.

“I think it really shows that if I’m attacking the zone with my stuff, the sky’s the limit for me. I just need to stay consistent with that. I’m still pissed about the two bombs. Obviously, you don’t want to give those up as a pitcher, but we got the win, so that’s all that matters.”

Harrison took the mound with an early 3-0 lead thanks to Chapman, who put the Giants on the board with a two-run homer to straightaway center field off Padres right-hander Joe Musgrove in the top of the first. His ninth-inning blast off reliever Pedro Avila was even more impressive, rocketing off his bat at 111.7 mph and hitting off the third deck of the Western Metal Supply Co. building in left field.

“It got out in a hurry,” Melvin said. “If it was any higher, it might have gone over the building.”

Chapman and fellow free-agent additions Jung Hoo Lee and Jorge Soler combined to go 6-for-14 with six RBIs and five runs, showcasing the collective firepower of the Giants’ new-look lineup. Chapman said it was extra satisfying to deliver a monster performance that resulted in a milestone win for Melvin, who also managed the star third baseman in Oakland.

“I think it’s definitely fitting,” Chapman said. “I was excited for him to get his first win. I know how badly he wants to win every single day. I didn’t want to make him wait too long. For me to be able to have a game like this means a lot. That’s a guy that I want to win for and do anything for, so it’s fun that it happened like this.”

Harrison opened his outing with three scoreless innings before misplacing a breaking ball that Machado blasted into the upper deck in left field to cut San Francisco’s lead to 4-1 with one out in the bottom of the fourth.

The Padres also threatened the following inning after Eguy Rosario sent a drive to right field that hit off the heel of LaMonte Wade Jr.’s glove, but Rosario ended up being thrown out trying to stretch a double into a triple. After allowing the ball to drop, Wade quickly threw to second baseman Thairo Estrada, who fired a one-hop throw to Chapman to nail Rosario at third.

“I think it was a great relay,” Chapman said. “Thairo can do it all.”

Harrison’s only other mistake came in the sixth, when he hung a changeup that Tatis smoked out to left for another solo blast, but he came back to retire Jake Cronenworth, Machado and Ha-Seong Kim to end his start on a high note.

The Giants will be leaning on Harrison to establish himself as a rotation mainstay in his first full season in the Majors, but they also know they’ll have to keep an eye on his workload since he never threw more than 113 innings in the Minors.

Despite Harrison’s low pitch count on Friday, Melvin opted to turn the game over to the bullpen in the bottom of the seventh and bring in fellow rookie Landen Roupp, who worked around a one-out single to Luis Campusano to post a scoreless inning in his Major League debut.

“There’s no real formula for innings,” Melvin said. “It’s more about seeing how [Harrison] feels from outing to outing and kind of going from there. The pitch count was under control. When you throw the ball over the plate, you’re going to give up -- especially to that team -- a homer or two. But if they’re solo home runs, you can live with it. He didn’t put himself in a position where there was a lot of traffic.”