SAN JOSE — Jackson Flora delivered the beer. Then got doused in sparkling apple cider.

The 21-year-old right-hander has barely begun his promising professional career with the San Francisco Giants, who selected him with the fourth pick two months ago, the first pitcher in the class. But a few of Flora’s attributes are already apparent after just two assignments since joining Low-A San Jose.

Flora has ace-level stuff. And he has a bit of ace-level showmanship.

The Bay Area native and UC Santa Barbara product was one heck of a playoff ringer for San Jose on Thursday night at Excite Ballpark. He topped out at 99.6 mph in two scoreless innings, landed his two breaking balls often enough, walked two, didn’t allow a hit, and struck out four — including Stockton Ports shortstop Edgar Montero, who was the designated “beer batter” in Game 2 of the California League Northern Division championship series.

The thirsty crowd chanted for the strikeout that would give them half-price suds, and when Jackson complied by blowing a fastball past Montero to end the second inning, the right-hander flamboyantly doffed his cap as he strutted off the mound.

“When I got two strikes on him, I figured I would let one eat, so that was fun,” Flora said. “I felt like I settled into a groove a little bit, getting those first two strikeouts in that (second) inning, and wanted to please the people. They were rooting for me, so I had to execute.”

Later, after the Giants finished off their series-clinching 3-1 victory, Flora joined his new teammates, some of whom are still teenagers, in blasting each other with Martinelli’s finest.

“I’ve never seen somebody hat-tip the stands after striking out the beer batter until today, and I’ve seen a lot of games in this ballpark over many years,” Giants farm director Kyle Haines said with a laugh. “But I thought that was a good play to the crowd there. Why not? Hat tip their discounted beer there.”

Flora’s professional experience this year will be more like a cup of coffee. He spent most of August working out at the Giants’ Papago Park minor league complex in Arizona, pitching in scrimmages and making refinements to a kick change that he hopes will complement his high-spin fastball, sweeper and shorter slider.

The Giants directed him to make his pro debut with an inning last weekend for San Jose, which was a dress rehearsal for the real assignment: a start in the best-of-three series against Stockton with the hope of reaching the Cal League championship series. After the Giants punched their ticket by sweeping two games from the Ports, Haines confirmed that Flora would take the ball one more time in next week’s best-of-3 series against Lake Elsinore.

Haines said the playoff assignment was about Flora’s mental development as much as his physical readiness.

“One (goal) is acclimating himself to the organization and competing with his new teammates, but also to experience what a playoff race feels like,” Haines said. “You just don’t know when you’re ever going to get these opportunities. A lot of players, including me when I was a young minor leaguer, thought it was going to happen regularly, and it doesn’t. … there’s value in winning together and feeling playoff baseball, and bringing out your inner competitor.

“And he showed that he can overwhelm just about anybody when his command’s on. He made some really good hitters on their other team look like they were in between pitches.”

Flora was the fourth overall selection of July’s Draft. (Al Bello / Getty Images)

Flora is the brightest pitching hope for a Giants farm system that now ranks among the best in the industry, yet remains heavily tilted toward position players. There is pitching in the system — left-hander Cesar Perdomo, who has allowed just one run in 10 innings since making his debut, is a good reminder that a strike thrower who can manipulate the baseball need not show up on top prospect lists to find major league success — but the beleaguered major league pitching staff requires so much help that it’s hard to imagine the Giants can do a credible overhaul in one offseason.

As tempting as it might be to think of Flora as an immediate fix, he’s as realistic as his coaches and coordinators. A lot of development needs to happen first.

“He’s very self-aware,” Haines said. “He told us a story about going to college and seeing the other players and evaluating what he needed to do. That was a pretty mature way for him to grow from a freshman into a sophomore. And I think we’ve seen a little bit of that here. He’s really good about realizing where the bar is and where he needs to get himself to, and he’s very driven, very competitive. You don’t always see that in players who might think they’ve got it figured out. He definitely doesn’t have it figured out, he knows he doesn’t have it figured out, and he’s got a lot to still get better at. But he’s also a really good competitor.”

And a crowd pleaser. Flora, who graduated from Foothill High in Pleasanton, the same high school that produced former Giants Gold Glove shortstop Brandon Crawford, had a sizable cheering section that included friends, family, his junior high coach and next-door neighbors. Some of them undoubtedly joined the hundreds of others who chanted “beer, beer, beer” once Flora got two strikes on Montero.

Flora needed an inning to settle in, missing the zone both arm side and glove side while issuing two walks in the first frame. He also struggled to land his changeup, perhaps because he grew accustomed to throwing it in the dry Arizona air. Catcher Rod Barajas Jr. helped Flora settle in by throwing out a runner attempting to steal second base.

After Flora completed his prescribed two innings, he remained in the dugout and cheered on his new teammates. Ricardo Estrada, a left-hander from Chihuahua, Mexico, tossed four solid innings. Two more international players — Taiwanese right-hander Chen-Hsun Lee and Venezuelan right-hander Samir Chires — combined to pitch the final three.

Exciting shortstop prospect Josuar Gonzalez lined a double to ignite San Jose’s two-run first inning, Estrada executed a pickoff that saved the Giants a run, and left fielder Oliver Tejada saved two more with a diving catch in the fifth. Designated hitter Drew Smith, a 14th-round pick in this year’s draft out of the University of Oregon, drove in all their runs with a two-run double in the first inning and a home run in the eighth.

“I don’t really feel like a new guy,” Flora said. “I feel like I’ve known these guys for a long time. …  It’s been really easy to come in here and be comfortable and hang out with these guys, which is awesome.”

San Jose pitching coach and former Giants left-hander Dan Runzler has only worked with Flora for a week. If Runzler returns to San Jose next season, it might be the only time he and Flora work together. Depending on how aggressive the Giants want to be with their assignments next season, the team could have a stacked rotation at High-A Eugene or Double-A Richmond with Flora, left-hander Jacob Bresnahan, and trade deadline additions Ramon Marquez and Henry Lalane.

“He’s definitely a routine-oriented guy,” Runzler said of Flora. “You can tell from the way he plays catch. Everything is really diligent. …  He’s very accountable for what he does, and he also asks a lot of questions, even as a young, newly drafted guy. And obviously, you guys see his stuff. It’s real.”

And the beer batter?

“I honestly think he just got in his element and did what he’s supposed to do, and was really fun to watch,” Runzler said.

Flora plans to return to Santa Barbara after the season, where he’s got three other newly drafted roommates to help keep each other on schedule with their winter workouts. He’ll take a few more classes as he whittles away the credits he needs to complete his degree in communications. And because he’s 21, he can buy something a little stronger than sparkling cider — even if he has to pay full price.

“To celebrate in the clubhouse like that just motivates you even more,” Flora said. “You want to get up to the big leagues and help that team win and celebrate like that on the big stage.”