After smooth traveling on the interstate over his previous four starts, Cincinnati Reds rookie pitcher Robert Stephenson hit a pothole and spun out of control Tuesday night. Stephenson won his previous four starts with a 2.08 earned run average, but the St. Louis Cardinals took him apart in Busch Stadium III on their way to a 13-4 undressing of the Reds. The Cardinals are on a late-season sprint as they try to catch the Chicago Cubs in the National League Central. By winning 11 of their last 14 they have pulled within two games of the division-leading Cubs. Stephenson survived only three innings and gave up six runs (five earned) and walked three. His problem Tuesday was an inability to retire the first batter in any of his three innings. Zack Cozart gave the Reds a 1-0 lead in the first inning with his 20th home run. He is the sixth Reds players this year with 20 or more home runs (Joey Votto, Adam Duvall, Scott Schebler, Eugenio Suarez), a club record. But by the time the Reds could score again against St. Louis starter Lance Lynn they were behind, 8-1. Stephenson walked Matt Carpenter to open the bottom of the first, one of four walks Carpenter drew from Reds pitchers. Tommy Pfam grounded to shortstop for a possible double play, but Zack Cozart’s throw to second was wide for an error and everybody was safe. Stephenson retired the next two but Yadier Molinia doubled double the left field line for two runs and a 2-1 Cardinals lead. Harrison Bader opened the second with a single and, once again, Stephenson retired the next two. But he walked Carpenter again and Tommy Pham tripled to right field for two runs and Paul DeJong doubled for another run and a 5-1 lead. Stephenson walked Molina to open the third and Kolten Wong doubled to left field. It quickly became 6-1 when Randal Grichuk hit a sacrifice fly. Alejandro Chacin replaced Stephenson in the fourth and apparently wasn’t paying attention to what kept getting Stephenson in trouble. He, too, put the first runner on base. He walked Carpenter, who is as tough to make swing at a bad pitch as Joey Votto. DeJong singled and Jose Martinez doubled for two more runs and an 8-84 Cardinals lead. The Reds broke through in the fifth with three runs and chased Lance Lynn. Scott Schebler doubled and slumping Adam Duvall, dropped from clean-up to seventh in the batting order, singled for a run. Pinch-hitter Patrick Kivlehan tripled for a run. Another run scored on a throwing error by the pitcher on a grounder by Jesse Winker. Winker, though, rounded first base too far and was thrown out trying to get back to first. But the Reds were back in the game, 8-4, until relief pitcher Rookie Davis gave up two runs in the sixth. DeJong led with a home run, his third hit of the night. Martinez singled, stole second, then scored on Molina’s single to make it 10-4. Ariel Hernandez started the seventh and, ugh, walked Greg Garcia to start the inning. That made it six out of seven innings that the first Cardinals batter reached base. Garcia scored when Carpenter finally swung the bat after his four walks. And he doubled for a run. Hernandez walked two more, his third walk of the inning, to load the bases. Pitching coach Mack Jenkins rushed to the mound for a tutorial. It didn’t work. Hernandez walked Carson Kelly, the Cardinals’ No. 1 catching prospect. It was Hernandez’s fourth walk of the inning and it forced in a run. Hernandez didn’t walk Kolten Wong. He singled to right field to make it 13-4 and Hernandez’s forgettable night was done. That signaled the major league debut of 6-foot-6 right handed pitcher Deck McGuire, called up earlier in the day from Class AA Pensacola — a tough bases loaded and one out situation. The 28-year-old McGuire was a No. 1 draft pick of the Toronto Blue Jays and the Reds picked him up in the minor league draft over the winter. McGuire is the 16th Reds player to make his major league debut, the 11th pitcher. And he is the 30th different Reds pitcher to appear this season. And he coaxed a double play ball out of Harrison Bader to mercifully end the inning. The Cardinals outhit the Reds, 14-9, and while Cincinnati pitchers continue to walk the world, Cardinals pitchers did not walk a batter until the ninth inning when they were up nine runs. In addition to getting whipped, the Reds lost second baseman Scooter Gennett. He left in mid-game with left hand inflammation.