The Colorado Rockies' performance on the mound is a big reason for their troubles.Jason Marquis will try to keep the Padres rolling and build on his own strong performance in the opener of a three-game set Friday night against the last-place Rockies.San Diego (39-55) has won five of six while its pitchers have compiled a 1.88 ERA in the last five games. That trend came to a head Thursday as Edinson Volquez tossed a one-hitter in a 1-0 victory over Houston, becoming the first Padre to accomplish such a feat at Petco Park.The Padres took three of four from the club with the worst record in the majors, and they'll try to continue taking advantage of a soft schedule at home when they face the team at the bottom of the NL West.Marquis (2-5, 3.62 ERA) is set to get the nod in the opener, and he'll be going for wins in back-to-back starts for the first time since May 2011 when he was with Washington. The veteran right-hander allowed two runs and six hits in six innings of a 7-2 win at Los Angeles on Sunday, breaking a stretch that saw him go 0-4 with a 4.60 ERA in five starts."Marquis did a great job," manager Bud Black said. "He was under the weather, battling stomach flu, and he didn't sleep well. But he really gutted it out on a day that he wasn't a hundred percent, physically. He stayed down in the tunnel between innings to cool off, but he hung in there."Marquis, who had a career high-tying 15 wins with Colorado in 2009, was charged with the loss in a 10-2 defeat against his former club on June 29, getting tagged for six runs in six innings.At the plate, Alexi Amarista has been pacing San Diego, hitting .387 with 16 RBIs and 13 runs in 17 games. He's managed at least one hit in all but one of those contests, and was 5 for 10 with two homers and four RBIs when the Padres took two of three at Coors Field from June 29-July 1.Unlike San Diego, the Rockies (35-56) continue to struggle getting outs. They have a majors-worst 5.26 ERA and have allowed an average of 6.4 runs in dropping four of five.The club will turn to rookie Drew Pomeranz (1-4, 3.79), who could use some help from his offense this time around if he's to beat the Padres for the first time in three meetings.The 23-year-old left-hander was impressive against them at home July 1, but was the hard-luck loser in a pitchers' duel with Kip Wells. Pomeranz allowed an unearned run and two hits in six innings of the 2-0 loss.He wasn't nearly as sharp in his first visit to Petco Park, a 3-2 defeat on May 7 that saw him allow three runs in three innings. He left in the fourth after sustaining a bruised right quad when he was hit by a liner off Volquez's bat.Pomeranz dropped his most recent outing Sunday, giving up five runs in five innings of a 5-1 loss to Philadelphia."What it boils down to is experience and awareness," manager Jim Tracy told the team's official website. "The teacher for that is him being in between the lines and going through (rough innings and situations). Drew Pomeranz will grow from this."The thing that continues to impress has been a much cleaner delivery and the adjustments he's made in regard to his arm slot."