DETROIT -- The Tigers entered Friday’s off-day ranked last in the American League in runs per game, batting average, strikeouts and Adjusted Batting Runs. They ranked next-to-last in runs scored, RBIs, slugging percentage, OPS and home runs. They’ve scored more than two runs in a game just three times, including Thursday’s 5-4 home-opener win over the Royals.

And yet, they entered Friday with a 5-3 record. They’re two games over .500 for the first time since May 5, 2017. They’re a half-game behind the first-place Twins in the American League Central. They’re one of just three teams who entered Friday with a winning record and a negative run differential.

The reason is clear: They’re pitching beyond anyone’s expectations.

Only the Rays entered Friday allowing fewer runs per game, fewer earned runs total and fewer hits per nine innings. Only the Blue Jays had more strikeouts. Detroit stands in the top three among AL clubs in ERA, WHIP ratio, strikeouts per nine innings and walks per nine innings. Tigers starters have induced more swinging strikes than any rotation in baseball, just ahead of the vaunted Astros rotation through Thursday, according to Statcast.

Detroit is doing this with a pitching staff that features just five All-Star selections combined -- only setup man Joe Jimenez more recently than 2014 -- and just three pitchers age 31 or older. None of the Tigers’ highly-touted pitching prospects have arrived yet; only Jimenez was a highly-rated prospect in recent years, and Spencer Turnbull is the Tigers’ 19th-rated prospect before he graduates from MLB Pipeline’s list later this month. Michael Fulmer is out for the year following Tommy John surgery.

How are the Tigers doing this? Can they possibly keep this up? While eight games provide a small sample size off which to judge, here are three key factors among the three starters with two outings already:

Zimmermann is healthy

One of the first things Jordan Zimmermann said in Spring Training was that he can’t pitch off his fastball anymore. That isn’t a revelation to many who watched him the last couple years. But this Spring Training, he was healthy enough to work on his pitches.

Even in just 13 2/3 innings over two starts, the results stand out. He’s throwing more sliders (39.6 percent) than fastballs (37.2) for the first time in his career, and he’s throwing his curveball (22 percent) more than ever. This is the mix he had going during a nice stretch back from the injured list last June and July before neck and core muscle issues hampered him over the second half.

Zimmermann’s slider has gotten better each season, but this year’s is by far his best. Opponents are just 2-for-24 off the pitch, whiffing on a quarter of them. His curveball has been a feast-or-famine pitch for him over the years, including five home runs and a 28.1 percent whiff rate last year, but it has been all stingy so far with swings and misses on nearly half of the 36 curves he has thrown so far. Both have been good putaway pitches.

Thus, while Zimmermann’s fastball is averaging just 90.7 mph thus far with a low spin rate, he mixes it in enough that hitters can’t sit on it.

Boyd slides into strikeout role

Since Matthew Boyd’s arrival in the David Price trade in 2015, the lefty has been known as a fastball pitcher dogged by big home runs. Through two starts this year, he’s a strikeout pitcher, with 23 of over just 11 1/3 innings. Only reigning NL Cy Young Award winner Jacob deGrom (24) had more strikeouts through Thursday.

The slider that was key to Boyd’s improvement last year has taken another step, responsible for 13 strikeouts in 67 pitches. Hitters are missing it at a 67.7 percent rate so far, compared with 33.1 percent last year. That rate won’t hold over a season, but the improvement should. The slider has a 2398-rpm spin rate so far, the highest of his career, while dropping to an average velocity of 78.6 mph. Meanwhile, his fastball spin rate is at 2409 rpm, up from 2282 last year, and is generating a 40-percent whiff rate and eight strikeouts.

Boyd had the benefit of late-afternoon shadows early in his last start Wednesday at Yankee Stadium, where he induced 26 swinging strikes out of 98 pitches. He did not have that advantage in Toronto last Friday, when he induced 19 swinging strikes in 85 pitches, including eight swing-and-misses on just 26 sliders.

Turnbull for what

Manager Ron Gardenhire went to bat for Turnbull in Spring Training, saying he had some of the best stuff of any pitcher in camp. Turnbull has backed it up so far, racking up 15 strikeouts over 11 innings in two starts. While his fastball has been hit for a .368 average, he has kept it in the park. Meanwhile, his secondary pitches have been better, including a curveball he spotted for four called strikes and two swings in just 13 pitches Thursday against the Royals. His cutter has been a good putaway pitch for him, racking up eight strikeouts and two balls in play out of just 34 pitches.