They're probably feeling at least a little regret, however, about what they gave up to get him.Cahill and red-hot Oakland Athletics rookie Jarrod Parker square off Saturday night at Chase Field in an intriguing matchup of pitchers who were traded for each other six months ago."It's cool how it worked out," Parker told the Diamondbacks' official website. "This is what everyone wants to see, right?"After winning the NL West last year, Arizona was in "go-for-it mode to stay on top of the division," according to general manager Kevin Towers. He tried to bolster the staff immediately by acquiring Cahill, an All-Star for the A's in 2010.Oakland, meanwhile, saw an opportunity to add an elite pitching prospect, sending Cahill and reliever Craig Breslow to the Diamondbacks for Parker, outfielder Collin Cowgill and reliever Ryan Cook on Dec. 9.Parker (2-2, 2.40 ERA), who made his major league debut Sept. 27 and pitched in Game 4 of the NL division series for Arizona, has emerged perhaps a bit sooner than expected following 2009 Tommy John surgery. He'll put an 18-inning scoreless streak on the line against the team that drafted him ninth overall in 2007.The right-hander took a no-hitter into the eighth inning Monday versus Texas, allowing only Michael Young's single before finishing the eighth in a 12-1 win."He's always going to have his stuff, it's just a matter of being consistent," catcher Kurt Suzuki told the Athletics' official website. "You're seeing it now. The more times he goes out there, the more comfortable he gets."Cahill (3-5, 3.45) was also sharp Sunday, with the sinkerballer inducing four double plays and completing a six-hitter in a 6-0 win at San Diego. It was an especially encouraging effort after he allowed four runs or more five times in his previous eight starts.He downplayed the reunion this week, but at the time of the trade sounded a little surprised after spending his first three major league seasons with the Athletics."I really liked Oakland, I was comfortable," Cahill said. "I definitely thought I'd be with them a little bit longer."A's manager Bob Melvin appreciates the serendipitous matchup."I think everyone looks forward to it, but we probably don't get caught up in it as much as the fans who have maybe rooted for both," Melvin said. "But there's definitely some intrigue to it."The trade favored Oakland (26-33) on Friday. Cook, who has allowed two runs and seven hits despite walking 15 in 26 innings this season, struck out the side in a scoreless eighth after Breslow allowed three extra-base hits -- including Seth Smith's two-run homer -- in the sixth.Arizona (28-30) had the last laugh when Ryan Roberts' three-run homer with two outs in the ninth ended a 9-8 win.That wasn't the only good sign in the Diamondbacks' third straight victory. The slumping Justin Upton was 2 for 4 after sitting out the previous two games and Paul Goldschmidt was also 2 for 4, extending his hitting streak to 15 games and connecting for his sixth homer during that run.Jason Kubel homered and is 5 for 10 with eight RBIs in his last two games.Even with the red-hot Yoenis Cespedes sidelined due to a hamstring problem, the A's continued their surprising offensive surge, scoring at least seven runs for the fourth time in their last seven contests. They're still last in the majors with a .218 average and last in the AL with 205 runs.