After San Francisco took two out of three from Colorado this week, there aren’t many make-or-break series remaining, but two rookies take the mound for the start of one on Friday night.

With four straight wins, the Minnesota Twins have moved within four games of the American League Central-leading Detroit Tigers, who are in Minneapolis for a three-game set this weekend.

The Tigers, who are 3-7 over their last 10 games, will give the ball to rookie Rick Porcello. The 20-year-old right-hander, who has been the youngest player in the majors nearly all season, leads the rookie class with 13 wins. He’s endured the ups and downs a young starter almost always faces in his debut season, but when he's been on -- as he was in May and August -- it's been obvious Porcello has a chance to be a No. 1 starter someday. He was 5-0 in May, when he posted a 1.50 ERA and .208 OBA in defeating Minnesota, Cleveland, Oakland, Colorado and Kansas City.

Porcello scuffled through the middle of the season, but after winning three of his last four starts, he has a chance to make a final push for AL Rookie of the Year honors. He worked six solid innings against Toronto in his last outing, and improved to 13-8 with a 4.21 ERA and .265 OBA. He hit 96 mph on the radar gun facing the Jays, and after the win, he discussed pitching in big games down the stretch.

“I didn’t know how I would feel in this situation -- I didn’t even know that I would be here,” Porcello said. “But I feel great. I just want to keep improving, because I don’t think I’m a finished product.”

If there’s an element of surprise to it for Porcello, consider how Twins rookie Brian Duensing must feel. Minnesota started the season with one of the youngest and most promising rotations in the game, but it’s been a rough year for Francisco Liriano and Glen Perkins, and Kevin Slowey was lost to a wrist injury in early July.

It wasn’t exactly a great year in the minors for Duensing, who for a second straight season posted a losing record with Triple-A Rochester and had a 4.66 ERA this year when he was promoted on July 3. He had a few rough outings out of the bullpen early on, but when Liriano was scratched with a sore forearm on July 29, Duensing gave the Twins five solid innings in a victory over the White Sox.

Duensing returned to the bullpen, but rejoined the rotation when another rookie, Anthony Swarzak, lost his starting job in late August. In five starts, with the Twins trying to hold on in the AL Central race, the 26-year-old left-hander has gone 3-0 with a 1.74 ERA and .250 OBA. He’s blanked two of his last three opponents, and after working seven scoreless innings in a victory over Oakland on Sunday, Duensing pitches the biggest game of his brief major league career.

The Tigers are 1-5 at the Metrodome this year, but the Twins will be without Justin Morneau, who is lost for the season with a stress fracture in his back. If the Tigers don’t put the Twins away this weekend, their four-game set in Detroit at the end of September may be just as meaningful.