Both offenses were improved in their series opener, but it was a big inning and the Rockies' supremacy in clutch situations proving to be the difference.Arizona hopes to take advantage of a shaky Roy Oswalt on Saturday night as it seeks just its third home victory in nine tries.The Rockies (68-80) had totaled 11 runs during the losses of a 1-5 stretch to start their nine-game divisional trip, while the Diamondbacks (73-73) came in with 12 runs over their last six games. They combined for 28 hits Friday but it was Colorado going 5 for 10 with runners in scoring position compared to Arizona's 2-for-12 performance as the Rockies won 7-5.Wilin Rosario was 2 for 5 and recorded two of his four RBIs in the Rockies' five-run seventh inning. The club's No. 1-5 hitters were a combined 12 for 25.Meanwhile, the Diamondbacks are 11 for 58 (.190) with men in scoring position over their last six."They walked us eight times," manager Kirk Gibson said, "and with all the hits we had (12) we should have scored more runs."They'll hope to have better luck against Oswalt (0-5, 8.57 ERA).The 36-year-old had spent two months on the disabled list due to a strained left hamstring he suffered in a 6-1 loss at Arizona on July 7, when he gave up a run and two hits in 1 2/3 innings before being injured.Oswalt made his return in relief duty on Sunday at San Diego but surrendered five runs, four hits and two walks in just 3 1/3 innings, suffering his fifth loss in as many appearances this season.He hasn't been able to catch many breaks as opponents are batting .470 on balls in play."The bad thing about it is, I'm running out of time to get arm strength back," Oswalt said. "I haven't had a lot of luck go my way."Getting the nod for Arizona will be Wade Miley (9-10, 3.37), who tries to snap a six-start winless stretch in which he's 0-2 with a 4.42 ERA while receiving only 3.19 runs of support per game.After throwing 1 2/3 innings two starts ago, he responded by limiting San Francisco to two runs and five hits over seven innings of a 3-2, 11-inning loss on Sunday."You can't worry about the last time out, you just go out and compete, give ourselves a chance to win," he said.Colorado could be just the opponent for him to notch his first win against since Aug. 6, as he's allowed one run in 12 1/3 innings over two starts against the Rockies this year. He's also 5-0 with a 2.52 in eight career matchups, including seven starts.Rosario is 5 for 11 off Miley with a homer and double.Oswalt is 9-4 with a 2.41 ERA in 14 career starts versus the Diamondbacks, last beating them in 2009.