With center fielder Jon Jay scuffling so far this season, Cardinals manager Mike Matheny said he’s not ready to commit to a platoon at the position. But Nats lefty Ross Detwiler did give him a reason to make a move. Shane Robinson, a righthanded-hitting alternative to Jay’s lefthanded swing, made his second start of the road trip in center and again hit atop the Cardinals lineup, the third different hitter to do so on this three-city trip. Both of Robinson’s starts this season have come against a lefthanded pitcher. “Makes it an easier decision to get Shane in there and give Jon a day,” Matheny said. “There is no question that he’s searching for a few things on the offensive side. We’ll give him some time to do that while he’s not still having to produce. It could be helpful speeding up the process.” Jay brought a .197 average into Tuesday’s game. He opened the road trip with a two-hit game in Pittsburgh and has since plummeted into a zero-for-21 streak. He has seven strikeouts in his previous seven at-bats. Jay had one of the best home averages in baseball last season (.384) and yet he struggled to hit on the road, at .224. This season he’s also two-for-16 (.125) against lefties. Robinson was the last of the position players to get a start this spring but one of the first for the bench to earn an increased role. The Cardinals entered spring training hoping to leave with a righthanded-hitter who could handle center field. Robinson made the choice for them by hitting .438 in the Grapefruit League with 18 runs scored and 12 extra-base hits.