For most of the season, Arizona's Wade Miley has made a convincing case for NL Rookie of the Year honors, but he's had a rough stretch in September.
It's been an impressive season for Miley (16-11, 3.32 ERA), who gets one more shot at joining five other pitchers - including CC Sabathia and Justin Verlander - as the only rookies to win 17 games since 1986.
However, after entering September with a 2.85 ERA, Miley is 2-2 with a 5.90 ERA in his last five starts. He gave up four runs and six hits in four innings of a 6-0 loss at San Francisco on Wednesday.
"I'm frustrated in myself," Miley said. "I wasn't locating my fastball and missing down."
Miley was attempting to become the first NL rookie to reach 17 wins since Cincinnati's Tom Browning in 1985.
The left-hander wasn't much better in previous start against the Rockies on Sept. 21. He allowed five runs and 10 hits - matching a season high - in six innings of a 15-5 win.
"I want to just go out and compete, and hope for the best and not put too much thought into (the game)," Miley told the Diamondbacks' official website regarding his final start. "I think that's what's gotten me into trouble lately, thinking a little too much. I just have to clear my mind and go out and compete like I did the first 25 starts."
He takes the mound after Arizona (80-79) took two of three from Chicago over the weekend. The Diamondbacks lost 7-2 Sunday after giving up four runs in the sixth.
Arizona is 9-6 against Colorado this season, winning three of four last week in Denver.
Paul Goldschmidt had two hits Sunday to extend his hitting streak to 10 games - he's hitting .361 (13 for 36) during that span - and is batting .321 (17 for 53) with two homers, seven doubles and 11 RBIs against the Rockies this year.
Colorado (62-97) comes to Chase Field having lost nine straight - and 14 of 15 - away from home. It was swept in Los Angeles over the weekend, losing 7-1 Sunday after being shut out in the previous two games.
There was one bright spot courtesy of Rafael Ortega, who had finished the season in Class-A Modesto and was playing in the Arizona instructional league when he was called up Sunday. The 21-year-old had two hits and reached base four times in his major league debut.
The Rockies, who have dropped 12 of 16 overall, have already surpassed the club record for losses. They haven't lost 10 in a row on the road since a franchise-record 13-game skid in 2008.
Colorado will hand the ball to Drew Pomeranz (2-9, 5.01), who went five scoreless innings in a 6-0 win over the Chicago Cubs on Wednesday.
The victory was his first since July 6, ending a 13-game winless streak.
"In the starts before I was trying to make too good of pitches. I tried to slow things down and keep it simple and throw strikes," Pomeranz said. "Let them hit it, let them get themselves out instead of trying to throw the perfect pitch."
The left-hander is 0-1 with an 11.05 ERA in two starts against the Diamondbacks this year, giving up nine runs in 7 1-3 innings.