McDonald will take the mound in the opener of a doubleheader against the Colorado Rockies, with Morton to follow in the second game as the Pirates look to build on one of their better offensive performances of the season.McDonald has allowed three runs or fewer in each of his first three starts, but he has yet to earn a victory as the Pirates have totaled seven runs in those outings.Morton is also winless after two starts in which he allowed a total of four earned runs while Pittsburgh scored four times.The Pirates (7-9) are ranked near the bottom in the majors in batting average, runs and homers, but they tied a season high in runs while recording double-digit hits for only the third time in a 5-4 win over Colorado on Tuesday night.Andrew McCutchen had three RBIs and Casey McGehee drove in the go-ahead run with an eighth-inning single."Being able to come back meant a lot, not only to our pitchers but also to the position players," McGehee told the Pirates' official website. "We've seen a lot of good pitching going by the wayside. Maybe they'll be able to breathe a little easier, knowing they don't have to be perfect every time out."Colorado's Carlos Gonzalez hit his first two homers of the season, both two-run shots, after missing three games last week because of strep throat."It felt good to hit a couple of balls hard again because it's been a tough couple of weeks," Gonzalez said. "I missed three games and that messed with my timing, and I had a bad fever for four days and that took away a lot of my strength. I just feel like I'm finally back to normal."McDonald (0-1, 3.45 ERA) will be looking to get back to normal after only making it through four innings because of a high pitch count in his previous start, allowing one run in a 2-1 win at Arizona last Wednesday.He threw 79 pitches, with 33 coming in the first inning."I can't let a young man throw 40 pitches in an inning," manager Clint Hurdle said. "It's command. It's repeating his delivery. It's getting strike one. ... We've got to get that thing down around 15 pitches an inning."McDonald threw 103 pitches in his only start against Colorado (8-8) last season, allowing five runs over 6 2/3 innings while not receiving a decision in a 6-5 home loss April 10. He had given up six runs in his previous six appearances versus the Rockies, going 3-1 with a 3.06 ERA.Juan Nicasio (1-0, 6.19) will oppose McDonald in his first appearance against the Pirates. The right-hander pitched well in his season debut but has allowed 10 runs in nine innings over his last two starts.He managed to earn a win last Wednesday despite allowing four runs and seven hits -- two homers -- over 6 1/3 innings against San Diego. It was Nicasio's first victory since being hit in the right temple by a line drive and suffering a fractured skull and broken neck Aug. 5."I'm happy," he said. "That (ovation) was good."Jhoulys Chacin (0-1, 4.80) will take on Morton (0-1, 3.60) in the second game as he looks to build on his best start of the season. The right-hander allowed four hits and three runs over seven innings in a 4-3 win at Milwaukee on Friday."His secondary pitches were that much better tonight because he was throwing strikes with his fastball," manager Jim Tracy told the Rockies' official website.Chacin is 1-2 with a 6.32 ERA in three starts against the Pirates, while Morton has gone 1-0 with a 4.15 ERA in three starts versus Colorado.