OAKLAND -- Hogan Harris stood at his locker inside the A’s clubhouse at the Coliseum last month and described his first call to the big leagues as feeling like a fantasy. A few hours later, however, that dream had turned into a nightmare.

Summoned from the A’s bullpen in a close game against the Mets on April 14, Harris endured one of the worst Major League debuts imaginable. After retiring Daniel Vogelbach on a groundout to begin the fifth inning, Harris walked five batters, hit another and gave up a double. Charged with six runs in just one-third of an inning, the left-hander became only the sixth pitcher (American League, National League or Federal League) since 1901 to walk five or more batters in his debut while pitching less than an inning. The next day, Harris was optioned back to the Minors.

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Recalled from Triple-A Las Vegas for the first time since that undesirable night, Harris enjoyed much more success in his second Major League appearance. Following opener Austin Pruitt out of the bullpen during a 6-3 loss to the Astros at the Coliseum on Saturday afternoon, Oakland’s No. 21 prospect bounced back with five scoreless innings, allowing just one hit and one walk with five strikeouts.

What was the biggest difference Saturday compared to his debut?

“I’d argue pretty much everything,” Harris said. “The biggest thing for me was just the fact that I was able to kind of find a rhythm again in Vegas. When I came up here the first time, I wasn’t doing too well in Vegas. It was kind of just that we needed somebody and, unfortunately, I wasn’t in the best state of mind.

“I was trying to figure things out. I was just kind of all over the place. I was able to find that rhythm down there and that changed everything for me.”

One obvious contrast was Harris’ strike-throwing ability. Against the Mets, just 14 of his 39 pitches went for strikes. This time around, he threw 54 strikes out of 77 pitches. Even his lone walk -- Martín Maldonado in the second inning -- was a competitive nine-pitch battle that featured three two-strike fouls before Harris missed with a fastball up in the zone for ball four.

It was a shift to more of an attack-the-zone mindset fueled by the experience of his previous outing with Oakland.

“One positive I took from the first one was that, even after all of it, there was really only one hit,” Harris said. “I just decided to attack and move from there. … Just keep it simple.”

Harris also showed off a new curveball he revamped during his recent stint in the Minors. Throwing it 17 times, he generated eight swings and three whiffs with it. The curve especially shined through in the sixth, when it produced an off-balance swing from Astros slugger Yordan Alvarez for strike three.

“I had the big slow curveball that initially was like 70, 71, 72 mph,” Harris said. “I switched to one that was a little bit harder. I threw it in practice, and I liked it. It gets more swings. That 70 mph one is just so slow that it’s tough to land in the strike zone consistently. That’s why I kind of switched to this harder one, and I’ve been getting a lot more swings on it.”

With the A’s carrying a starting rotation that entered Saturday holding the highest ERA (7.19) and second-most walks (121) in the Majors, Harris’ performance bodes well for his opportunities to establish himself at the highest level.

“His first outing was a tough one,” said A’s acting manager Darren Bush. “I’m sure he’s gone down and thought about what he could do differently. Today, he came out and attacked. He had command of all his pitches. He went right at them. That is going to be a huge confidence booster for him.”