Each sends a highly regarded young hurler to the mound Tuesday night, with Michael Wacha looking to guide St. Louis to an eighth victory in 10 tries in a matchup with Tyler Skaggs and visiting Arizona.St. Louis (38-19) has the best record in the major leagues and hasn't lost back-to-back games since a three-game skid April 27-29. Carlos Beltran went 3 for 5 with a two-run homer and Yadier Molina, after appealing a one-game suspension handed down just before the contest, hit a solo homer in the fifth inning of a 7-1 win over the Diamondbacks on Monday.Matt Carpenter had three hits and is batting .412 during a career high-tying 12-game hitting streak.The defeat was the first in three contests for Arizona (32-25). Gerardo Parra, 10 for 20 in four games versus St. Louis this season, had two hits and is batting .407 during a seven-game hitting streak.Both teams' success to date is due largely to strong pitching. St. Louis has a 2.96 ERA that's tops in baseball, while Arizona ranks seventh with a 3.64 mark.Skaggs (1-0, 0.00 ERA) contributed to that number in his first start of the season May 27. Called up to start the first game of a doubleheader, he gave up three hits and struck out nine in six scoreless innings of a 5-3 win over Texas."I'm happy that they called me up and had the confidence in me," said Skaggs, who went 1/3 with a 5.83 ERA in six starts last season. "Hopefully I opened up a few eyes."Though the Diamondbacks initially recalled Randall Delgado to take the roster spot of Brandon McCarthy, who was placed on the disabled list with shoulder inflammation, manager Kirk Gibson opted to give the 21-year-old Skaggs another start."He threw all of his pitches. That's what he has to do, and hopefully he'll do that again," Gibson told the team's official website.The left-hander, Arizona's top prospect according to MLB.com, has not faced the Cardinals, who will start a prized youngster of their own.Wacha (0-0, 1.29) had impressive major league debut Thursday, allowing one run and two hits while striking out six in seven innings of a 4-2 loss to Kansas City. The bullpen allowed three ninth-inning runs."Definitely just one to remember," Wacha said. "Once I threw the first pitch for a strike I really calmed down and was able to execute my pitches pretty well."The right-hander will face a Diamondbacks team that has dropped five of six in St. Louis.Arizona had won three of the previous four meetings overall prior to Monday.