Giants’ patience with draftmates Mac Williamson, Chris Stratton paying off

Photo: Jayne Kamin-Oncea / Getty Images ANAHEIM, CA - APRIL 20: Mac Williamson #51 of the San Francisco...

Six years before Mac Williamson tilted the Wow Scale with his 464-foot homer to right-center field at AT&T Park on Tuesday night, Giants scouting director John Barr had seen the same animal strength while sitting in the stands at Wake Forest looking for hitters to draft.

“We didn’t have the ability to see exit velocities then,” Barr said with a laugh Tuesday, “but we knew he had power.”

In the same winter and spring, Barr and his army of amateur scouts also saw a wiry kid at Mississippi State throw curveballs that they were sure big-league hitters would miss, and a left-hander from Creighton who did not light up the radar gun but threw strike after strike and made more starts than any collegian that season.

The first was Chris Stratton, the second Ty Blach.

When Williamson homered in games against the Nationals on Monday and Tuesday nights, the first started by Stratton, the second by Blach, Giants fans happily witnessed the perseverance of the players and the patience of the organization.

The Giants selected all three near the top of the 2012 amateur draft. Stratton was their first-round pick, taken 20th overall. They grabbed Williamson in the third round and Blach in the fifth.

None reached the majors quickly. Fans and scouts began to label Stratton a “bust.” Williamson earned the insulting sobriquet of a “four-A player” who could dominate the highest level of the minor leagues yet not hit big-league pitching.

Blach was the first to make an impact. He beat the Dodgers with eight shutout innings in the final series of the 2016 regular season to help the Giants secure a playoff spot.

Photo: Ross D. Franklin / Associated Press Giants starting pitcher Chris Stratton ranks ninth in the National...

The 2012 draft was shaping into one of the weakest of Barr’s tenure, which began in 2008 when he selected Buster Posey with the fifth overall pick. Even now, only six picks from that draft have reached the majors. The most successful, by Wins Above Replacement, is Matt Duffy, who was traded and has had just one good, healthy season.

The organization stubbornly held onto hope that Stratton and Williamson could contribute to winning baseball in the majors. The Giants continued to protect them with precious 40-man roster spots as younger prospects rose through the system.

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“I think we’ve been very loyal to our signees to get them as much of a resume as they can in the minor leagues before they get into the big leagues,” executive vice president of baseball operations Brian Sabean said. “We’ve also been spoiled because we’ve had a lot of position players and pitchers who spent little time in the minors and became established before what was expected of them.”

Stratton was drafted with outsized expectations because he was the reigning SEC Pitcher of the Year, and because the Giants had such a great track record picking pitchers in the first round and getting them to the majors quickly (Matt Cain, Tim Lincecum, Madison Bumgarner).

Williamson was the holy grail for power-starved fans frustrated by the Giants’ inability to draft and develop big-hitting outfielders over not just years, but decades.

Giants starter Chris Stratton, a 2012 first-round pick, is ninth in the National League this season with a 2.32 ERA. Giants starter Chris Stratton, a 2012 first-round pick, is ninth in the National League this season with a 2.32 ERA. Photo: Santiago Mejia / The Chronicle Photo: Santiago Mejia / The Chronicle Image 1 of / 7 Caption Close Giants’ patience with draftmates Mac Williamson, Chris Stratton paying off 1 / 7 Back to Gallery

Sabean said Williamson possessed the “size, strength and power bat that’s very difficult to trade for. It’s almost impossible to trade for power. It’s even more impossible to sign in the free-agent market. You have to wait to see how that comes to fruition.”

Both had to overcome significant injuries early in their development as well.

Stratton’s debut season as a pro ended after eight games in the short-season Northwest League when he was smoked in the head by a line drive during batting practice and sustained a concussion.

Williamson, a former pitcher converted to the outfield in college, needed Tommy John surgery to reconstruct his throwing arm in 2014, a year after he hit 25 homers and dominated the California League at Class A San Jose. Minor injuries dogged Williamson even after he reached the majors.

Stratton was erratic in the minors and made a breakthrough when he began to trust his fastball and consistently throw it for strikes. That and his moneymaker curveball have proven to be a tough combination for big-league hitters.

Stratton ranks ninth in the National League this season with a 2.32 ERA, giving the rotation a huge lift in Madison Bumgarner’s absence. Stratton also has the fourth-lowest ERA in the majors at 2.38 since Aug. 5, when he joined the rotation full-time.

Williamson didn’t hit when given a chance in the majors, starting in 2015. Some say the Giants didn’t give him consistent opportunities. Either way, the stat sheet showed nine home runs, a .226 batting average and 68 strikeouts in 212 at-bats. When he wasn’t striking out, he was pounding the ball into the ground.

Then, after overhauling his swing over the winter with private coach Doug Latta to increase his plate coverage and generate more lift, Williamson began to crush it. He hit 10 combined homers in spring training and at Triple-A early this season, earning his call-up to a big-league club that needed him.

Williamson’s sample size is tiny. He has played just five big-league games this season, but the three tape-measure homers he hit to propel the Giants to consecutive series victories over the Angels and Nationals have raised the optimism level.

“It’s about being consistent for a long period of time,” manager Bruce Bochy said. “I love his mechanics and the hard work he put in. It isn’t just this week. He had a good spring swinging the bat and he’s already shown it’s something he can maintain. Knock on wood, it will continue.”

Henry Schulman is a San Francisco Chronicle staff writer. Email: hschulman@sfchronicle.com Twitter: @hankschulman