With their rotation struggling to withstand depth issues behind co-aces Logan Webb and Alex Cobb all season, the postseason-hopeful Giants are calling in a top-rated reinforcement. The team is promoting No. 1 prospect Kyle Harrison to replace the injured Ross Stripling in San Francisco’s rotation, manager Gabe Kapler confirmed over the weekend.

• Giants calling up No. 1 prospect, LHP Kyle Harrison

The No. 20 overall prospect per MLB Pipeline, Harrison will be thrown right into the playoff hunt and make his MLB debut Tuesday in Philadelphia against the Phillies, who entered the week two games up on the Giants for the National League’s top Wild Card spot. Harrison is the sport's top left-handed pitching prospect and the second-best pitching prospect overall, per MLB Pipeline.

• MLB Pipeline | Top 100 prospects | Prospect video

“The last couple outings, I think he’s taking some real steps forward,” Kapler told reporters in Atlanta this weekend. “We think he’s ready to come up and help us win baseball games. That’s like the most important thing.”

The Giants’ third-round pick (85th overall) in the 2020 Draft, Harrison was widely considered the best healthy prep left-hander in the ‘20 class coming out of Bay Area Concord High that year, before falling due to signability issues. San Francisco dispelled those concerns by signing the local kid for first-round money -- a $2,497,500 bonus -- then watched his arsenal take immediate steps forward upon his debut at Low-A San Jose the following summer.

Harrison earned Low-A pitcher of the year honors in his pro debut, leading the league in ERA (3.19) and strikeouts per nine (14.3) in 2021. The results were even better last year, where Harrison led the Minors in whiffs per nine (14.8) and whiff percentage (39.8) while reaching Double-A as a 20-year-old. Harrison’s results were more mixed this season at Triple-A Sacramento, where he posted huge strikeout numbers (105 punchouts in 65 2/3 innings) but also his highest walk rate (6.6 per nine) and ERA (4.66) as a pro.

Harrison’s low three-quarter arm slot creates good angle and shape on his pitches, and when he’s in the strike zone, his enhanced stuff makes him electric. He has the ability to miss bats in the strike zone with all three of his pitches: a low-to-mid-90s fastball with riding action that can touch 97 mph, a plus low-80s slider with sweep and a fading mid-80s changeup that helps Harrison neutralize right-handed hitters. It's that advanced stuff that has made Harrison the Giants' most anticipated pitching prospect since Madison Bumgarner.

It’s also developed at a faster pace than Harrison’s control and command; at the lower levels, that stuff was overpowering enough for Harrison to get away with mistakes when he made them. That kind of impunity doesn’t exist in the Majors, and the Giants know that. Which is why they were super encouraged by Harrison’s last two appearances with Sacramento, where he racked up 11 strikeouts without a walk across 7 1/3 innings. The timing of his promotion is not coincidental, coming off those two strong outings.

Not long ago, the thinking was that once Harrison refined his control and command he’d be a strong candidate to headline the Giants' rotation for years to come. That still might be the case. But San Francisco needs him now. The Giants aren’t expecting the 22-year-old to be a complete panacea -- Harrison still isn’t fully re-stretched out after missing most of July with a right hamstring strain -- but they are hoping he can provide a jolt with quality innings down the stretch.

It’s not out of the question that Harrison could stick around once Stripling returns, either. San Francisco recently lost No. 3 starter Anthony DeSclafani for probably the remainder of the season, and the club has been relying on openers and bullpen days to cover that void.