Photo: Michael Macor / The Chronicle Photo: Ezra Shaw / Getty Images

Joe Panik isn’t any bigger. He isn’t any stronger. He hasn’t adopted Giancarlo Stanton’s weight-training program. He’s not obsessed with launch angles or exit velocities. He hasn’t developed an upper-cut swing or assumed a long-ball-or-bust philosophy.

Really, he’s the same Joe Panik.

“Still 6 foot, 200 pounds,” he said.

Except for one little factor. He has three home runs in the Giants’ first five games. The first time in his life he has homered three times in a season’s first week.

Panik’s latest came in the fourth inning of Tuesday’s home opener, a 6-4 loss to the Mariners. Last year, he hit his third homer June 8. In his 58th game. He finished with 10, tying a career high.

Could Panik increase his output to 15 or 20 this year?

“I’d say 60,” manager Bruce Bochy said. “I’m not going to cut him short.”

Naturally, the quip was relayed to Panik, who said, “All I can do is laugh at that one. Listen, I’m going to stick to who I am. If the opportunity presents itself, I’m going to take my shots here and there.”

The Giants are all in. But three homers in 19 at-bats? Why the power barrage? This is a top-of-the-order second baseman who homered just 29 times in 1,626 at-bats his first four seasons.

What gives?

Here’s what gives: Panik made a mechanical adjustment that has helped his approach, physically and mentally. Midway through spring training, the Giants’ new batting coaches, Alonzo Powell and Rick Schu, suggested Panik move his front (right) foot slightly inward.

The purpose is twofold. No. 1, it keeps Panik in a closed stance longer, making it less likely he’ll open up and be exposed on certain pitches. No. 2, it gives him confidence to aggressively drive the ball early in the count.

Powell and Schu realized Panik is tough to strike out. In fact, for the second straight year, he had the majors’ lowest strikeout rate, averaging one K every 9.5 at-bats. Nobody was close. The Angels’ Andrelton Simmons was second at 8.8.

So the hitting coaches figured Panik was the perfect guy to make the adjustment.

“It puts him in a better position,” Powell said. “He was a good hitter before we got here. We thought he could be able to take advantage of being a little more aggressive early in the count because he’s got a good two-strike approach, as we all know. We saw it work in Houston a little bit with Altuve. … ”

(We interrupt this quote to ask, “Wait, Altuve? Jose Altuve, the Astros’ dynamic second baseman?” Yes. Powell was their assistant hitting coach last year.)

“ … I’m not going to put him in the same category as Altuve. It’s not fair to Joe. But so far, so good, and hopefully he can stay with it.”

That’s the plan.

“It’s very early, but I’m very happy with the adjustments I made in the spring and kind of carried over to the season,” said Panik, who’s 8-for-19 (five singles, too) with only one strikeout. “Right now, just trying to ride the wave while it’s hot.”

This isn’t simply about a left-handed batter teeing off on a right-hander’s misplaced fastballs. Consider the variety of pitches Panik has taken deep:

A 2-2 fastball from Clayton Kershaw, a lefty.

An 0-1 cutter from Kenley Jansen, a righty.

A 2-1 changeup from Marco Gonzales, a lefty.

“I’m able to stay on pitches from lefties and get my hands through a cutter from a righty, which is always a tough pitch to get to,” Panik said.

Many hitters have altered their launch angles based on the new-school analytic method of driving the ball, but Panik is more concerned about backspinning, which elevates balls he pulls, an old-school approach to hitting.

If Panik were caught up in launch angles, he said, a ball hit to the left side would be a flyout, not a line drive. He realizes he doesn’t have the power for hitting opposite-field homers.

“Lot of stuff now. Lot of numbers. Lot of analytics,” Panik said. “For me, I’m a feel hitter. You’re your best hitting coach. You have to know your body, you have to know your swing. That’s having to feel it, not just going off numbers. You use those as a supplement.”

For the season’s first 42 innings, Panik’s three solo homers accounted for all the Giants’ scoring. Evan Longoria finally got his first hit, a two-run homer in the seventh, and the Giants scored once more in the eighth.

Panik was pleased to see the Giants rally from a 6-1 deficit and has confidence in the offense despite the slow start. Meantime, he’ll continue with his batting approach, and he’s perfectly fine if it’ll lead to some more home runs this year.

Even if he doesn’t hit 60.