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Danny Duffy would not be J.D. Martinez's favorite pitcher to face. The two met plenty of times in the American League Central. The first time, back in 2014, Martinez homered. In 23 plate appearances against Duffy since then, Martinez is 2-for-21 (.095) with no home runs and nine strikeouts.

You might say Duffy has Martinez figured out. And here's what he has figured:

"He seems to have really mastered his craft," the Kansas City Royals left-hander said this week. "He's a master of his gift. It's fun to watch, and on top of all that, he's a really good guy, too."

OK then. So even the guy Martinez struggles to hit realizes he is a pretty special hitter. And maybe we shouldn't be surprised by what Martinez has done in the 71 days since the Arizona Diamondbacks traded for Martinez in July. And maybe we should all take a moment off from watching Giancarlo Stanton and Aaron Judge to see what J.D. Martinez is doing out there in Arizona.

What he did Wednesday was follow a two-run first-inning double with a second-inning grand slam as the Diamondbacks beat the Giants. What he has done since that July 19 trade with the Detroit Tigers is hit as many home runs as anyone in the major leagues. Martinez and Stanton each have 28 since then, and while it took Stanton 280 plate appearances to hit his, Martinez has his 28 in just 243 plate appearances.

Surprised?

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"I'm not," Duffy said.

Some other people must be, given how few teams made any real attempt to trade for Martinez when the Tigers put him on the market in July. Tigers general manager Al Avila told reporters (including Chris McCosky of the Detroit News) his options were "somewhat limited," which is a nice way of saying no one but the Diamondbacks was offering anything (and they weren't offering much).

Good for the Diamondbacks and first-year general manager Mike Hazen, who wanted to find someone to hit behind star first baseman Paul Goldschmidt and ended up with a guy who has outdone Goldschmidt in the second half. Goldschmidt's numbers since the trade have been outstanding (.285/.371/.565, with 15 home runs and 49 RBI in 60 games). It's just that Martinez's have been arguably the best in baseball (.303/.370/.752, with 28 home runs and 64 RBI in 58 games).

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"He's been everything we'd hoped for and then some," D-backs manager Torey Lovullo said a few weeks back.

You'd have to believe some of those teams that passed on Martinez in July will be more interested when he becomes a free agent this winter. You'd have to believe plenty of them would rather not face Martinez and the Diamondbacks when the postseason opens next week.

The D-backs will be there for the first time since 2011, hosting the National League Wild Card Game Oct. 4. They'll be a dangerous opponent for whoever they meet, most likely the Colorado Rockies in the Wild Card Game and the Los Angeles Dodgers if they advance to the division series.

The Dodgers might remember Martinez. He's the guy who hit four home runs against them. In one game.

It was Sept. 4, it ended 13-0 to the Diamondbacks, and it began the D-backs' second three-game sweep of the Dodgers in two weeks. It wasn't long after that Jon Heyman of FanRag Sports quoted a rival official saying the D-backs were "simply a better team [than the Dodgers] right now."

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It's not all Martinez. Robbie Ray came back from a month on the disabled list and has a 2.45 ERA in six starts, all of them Arizona wins. Reliever Archie Bradley has a 1.23 ERA since the start of August. Fernando Rodney has converted 18 of his last 19 save opportunities. Goldschmidt is a top candidate to be the National League's Most Valuable Player.

But Martinez was the one big midseason addition, and he's the one who has been the biggest difference-maker in the second half.

Not that it should come as a surprise. Two years ago with the Tigers, Martinez hit 38 home runs. In the first half of this season, he homered 16 times and had a 1.018 OPS.

"You could seemingly throw a four-seam running in to him at his kneecap, and he'll find a way to hit it out to right field," Duffy said.

Duffy knew it. Apparently the Diamondbacks did, too. They won't worry that other teams didn't.

They have Martinez, they're in the playoffs and some of those other teams aren't.

Danny Knobler covers Major League Baseball as a national columnist for Bleacher Report.

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