CINCINNATI -- Coming off Sunday's win, the Reds got Jonathan India back from the injured list before the opening of their series vs. the Padres. Pitcher Reiver Sanmartin appeared to be off to a promising start his first time through the lineup and his offense gave him an early lead, in part, thanks to a quirky mistake by Padres catcher Austin Nola.

Soon though, it all turned against Cincinnati and Sanmartin when an interminable top of the fourth inning notched eight runs during a 9-6 loss to the Padres. Sanmartin faced eight batters in the rally, and all reached safely on seven hits and a walk as his club dropped 12 of its last 13 games -- including all four vs. San Diego.

From good fortune back to misfortune, just like that.

First, the good. As Colin Moran was up with two outs in the second inning, Nola threw a ball back to Musgrove that hit Moran’s bat and skipped away for an error that moved Nick Senzel to second base. The error, charged to Nola, then allowed Senzel to score the game's first run easily on Moran's blooped single to left field.

Effectively mixing his changeup and sinker, Sanmartin opened the game by retiring nine of his first 10 batters. His only blemish was Ha-Seong Kim hitting a first-pitch fastball for a game-tying solo homer to left field.

It went awry in the fourth inning when the Padres really started hitting, and hitting some more. The third hit of the frame was Jurickson Profar's RBI double to right field. Next, Eric Hosmer slugged a 1-0 changeup for a three-run homer and a 5-1 San Diego lead.

"He's a sinker baller," Padres manager Bob Melvin said of Sanmartin. "He's got a high ground-ball rate, his changeup plays off of that, his breaking ball spins to the other side of the plate. So he was kind of commanding the bottom of the zone. We were trying to get him up ... we got some balls up in the zone and certainly Hosmer's was the big blow of the inning. But you know what, the bats just seemed to get better the more we strung them along and passed the baton to the next guy."

Two infield hits sandwiched a bloop single to load the bases before Kim walked to force in a run to end Sanmartin's night.

Sanmartin threw 62 pitches, including 25 changeups -- with nine either being called strikes or whiffs according to Statcast.

"He knows what makes him successful," Reds manager David Bell said. "It’s really important for him to locate his pitches. He has nice movement on a few different pitches, but to locate is really what makes him successful. He was doing that. He just has to continue to do it. Don’t get away from it now. The results were not what he wanted, but he just has to keep trusting what he does. When he does it, he’s going to have a lot of success here."

Long reliever Jeff Hoffman inherited the trouble and gave up a bases-clearing triple to right field by Jake Cronenworth to make it a 9-1 game. Sanmartin was charged with a career-high nine earned runs and eight hits over three-plus innings with a walk and two strikeouts.

"Really, Reiver located his pitches pretty well," Bell said. "He was kind of right on the edges, even maybe some balls that were hit, he was getting some soft contact and those balls were going for hits and that made it tough for him. Then, I guess the big home run by Hosmer. All-in-all, he was really making pitches, just made it difficult for him with some of those hits finding holes."

In four games, Sanmartin is 0-3 with a 10.91 ERA. He allowed five or more runs in all three of his starts. The Reds used an opener in his other outing, on April 14 vs. the Dodgers, before Sanmartin pitched five scoreless innings.

Sanmartin is one of three rookies in a young Reds rotation that also includes prospects Hunter Greene and Nick Lodolo. The club is eyeing the return of ace Luis Castillo in the coming weeks. Castillo is one start into a rehab assignment in the Minors and will likely get two more starts before he would be activated.

In the meantime, the club wants to encourage Sanmartin to keep working.

"Especially the way he pitches, a lot of it is with his confidence, so we've got to make sure that that doesn't waver because he's going to keep getting opportunities to pitch for us," Bell said.