DETROIT -- Edwin Jackson built his breakout season on the combination of a power fastball and a nasty, biting slider. He rode that duo all the way to the All-Star Game, and he won several low-scoring games doing it. As the 2009 season wraps up, those scores are rising, as maybe are Jackson's sliders.

It wasn't long ago this summer that Jackson was on Zack Greinke's heels among the American League ERA leaders. Their anticipated pitching duel in Thursday's series finale between the Tigers and Royals never quite materialized, but damage to Jackson's pitching line did in a hurry, sending Detroit on its way to a 9-2 loss Thursday afternoon at Comerica Park.

The loss not only sent the Tigers to a series defeat, but it also dropped their lead in the American League Central to four games against the idle Twins, who await the division leaders at the Metrodome for a three-game showdown starting Friday night.

A look beyond the standings, meanwhile, shows Detroit has now allowed as many runs as it has scored this season. No other team with a .500 record or better has a zero run differential. It generally means the Tigers have won a lot of close games and lost more than a few by large margins.

Thursday's game fell into the latter category thanks to Alberto Callaspo's two-run double in the first inning and Miguel Olivo's three-run homer in the third. Both came against Jackson (12-7), who recovered to retire the final eight batters he faced to get through five innings.

Jackson won't pitch this weekend against Minnesota, but he's slated to start Tuesday's series opener at Cleveland. It's likely Detroit will work on his mix of pitches between now and then.

"It seems like he's pitched quite a few games without all his ammunition," Leyland said. "He hasn't had his breaking stuff on any consistent basis for quite a while."

Asked how long he felt Jackson had been pitching like that, Leyland pointed to Jackson's stats since the All-Star break, including a 5-3 record, 4.79 ERA and .357 on-base percentage allowed.

A targeted split, however, might be his past five starts. Jackson has allowed 21 earned runs on 37 hits over 31 1/3 innings in that span, and his ERA has risen a half-run from 2.86 on Aug. 21 to 3.37 now.

Both run-scoring hits off Jackson came on fastballs, but they were the only big hits he allowed all day. Both came with runners on base thanks to smaller plays ahead of them.

Jackson may have had the side retired in the opening frame, but a ground ball he got on a slider to Billy Butler turned into a fielder's choice and no outs, when Ramon Santiago tried to flip to second to force out Willie Bloomquist instead of throwing out Butler at first. Two batters after Bloomquist beat the throw, Callaspo got a 94 mph fastball up and drove it to left-center.

Butler's leadoff single to center on a 95 mph fastball was the catalyst behind the third-inning rally. Jackson fell behind on back-to-back sliders and lost Callaspo to fastballs on a four-pitch walk that put runners at first and second for Olivo, who got a 94 mph fastball over the plate and drove it 422 feet to straightaway center for his 21st home run of the year.

"Some of those hits they got were E.J. missing on some good pitches," catcher Alex Avila said. "Some bloops here, and a walk, and then they were able to get a big hit. It was a frustrating day."

Jackson told reporters afterward that he felt healthy, that he might've been rushing his mechanics and losing command on his sliders. Others wondered whether he was losing confidence in his secondary pitches or simply overthrowing.

"He doesn't have a good feel for it right now, for whatever reason," Leyland said, "so he probably doesn't have the confidence. But for the first half, the slider was devastating. It hasn't been there on a consistent basis the second half for whatever reason. I don't know."

The resulting run support was plenty for Greinke (14-8), who struck out five of the first seven Tigers he faced, three of them on called third strikes, on his way to eight strikeouts from the 19 batters he faced. He scattered three singles and two walks, but Curtis Granderson was the lone Tiger to reach scoring position. That opportunity vanished when Greinke retired Carlos Guillen for an inning-ending groundout.

Once former Tiger Josh Anderson essentially put the game away with a three-run homer off Armando Galarraga in the seventh, the Tigers went to their reserves. From there, they hit the road.

"When you're replacing guys, your regulars, in the sixth or seventh inning in two out of three games, that's usually not a good sign," Leyland said.