The Diamondbacks returned from a 4-2 road trip last week feeling pretty good about themselves and their postseason chances. They were nipping at the heels of the Padres and heading home for a nine-game homestand and an opportunity to make up ground in the standings. And when they beat the Rangers handily last Friday night, it seemed like maybe they were ready to take off. Since then, though, it’s been a struggle for the Diamondbacks. The 4-3 loss to the Marlins on Wednesday night was their second straight and their fourth in their last five games. If not for a late-inning rally Monday night for a walk-off win they would have lost five straight and been in dire straits in the postseason chase. As it is, the loss, combined with the Padres’ win over the Rockies, dropped the Diamondbacks to 3 1/2 games behind San Diego for the final National League Wild Card spot with nine games left to play. The two teams will face each other in a three-game series to close out the regular season at Petco Park.