PHOENIX -- Since the calendar flipped to May, the Marlins’ fortunes have turned the wrong way. They went 12-8 in April and finished on a seven-game winning streak, rolling into the new month.

Now, Miami’s in a slump, ending up on the losing side of a plethora of close games. But manager Don Mattingly remains optimistic for his club. He even gave himself a rare reminder early Monday of how much baseball there is still left to play.

“We’re going to definitely continue to stay upbeat,” Mattingly said. “I’m not someone who looks at standings, but today I looked at the standings and I’m like, ‘OK, 134 games left.’ Actually, we’re playing pretty good baseball.”

There was some good baseball played by the Marlins at times on Monday night. But, again, it resulted in a one-run loss, as they fell, 4-3, to the D-backs in the opener of a three-game series at Chase Field. Ketel Marte lifted Arizona with a tie-breaking solo homer in the sixth inning.

Miami has lost eight of its past nine games -- its seven most recent defeats each coming by a margin of only one run. The Marlins’ 15 one-run games this season are tied with the Blue Jays for the most in baseball, and their 10 losses in such contests are an MLB high.

“It’s just a matter of staying positive,” starter Elieser Hernandez said through an interpreter. “Continue battling, and things will come out right.”

There were some positives during Monday’s loss:

• Hernandez settled in after allowing three runs over the first two innings. After giving up a leadoff single to Christian Walker in the third, Hernandez retired the next 10 D-backs batters, a stretch that ended with Marte’s homer on the righty’s 88th and final pitch of the night.

“I was battling, I stayed in the game and continued to try to keep the team in the game,” said Hernandez, who fanned five over 5 1/3 innings.

• Miami twice showed the ability to respond on offense. It orchestrated a two-out rally in the second inning that resulted in Jacob Stallings’ game-tying two-run single. And after Arizona immediately took back the lead in the bottom of the inning, Garrett Cooper knotted the contest again with a solo homer in the fourth.

• Avisaíl García went 2-for-4 with a pair of singles, the second time in 25 games this season in which he’s had multiple hits. His only previous multi-hit game was a two-hit showing vs. the Braves on April 23.

If the Marlins can get hitters such as García (.189 average), Miguel Rojas (.188) and Jorge Soler (.174) going, they’d have a better chance of breaking open these close games.

• Tommy Nance impressed in his Miami debut, striking out three in 1 2/3 hitless innings of relief. The 31-year-old right-hander could be another valuable option for the Marlins out of the bullpen, should he have more showings like this one.

“I think it’s really good to build off of,” Nance said. “There are still things that I want to improve on and get better at, but it’s definitely nice having a successful first one.”

Despite those bright spots, the Marlins missed late-game opportunities to break through and potentially put this tough stretch behind them. They had runners on first and second with one out in the eighth and didn’t score. And they couldn’t capitalize on García’s leadoff single in the ninth, with Rojas hitting into a game-ending double play.

Mattingly noted this recent string of one-run losses has been “obviously a little bit frustrating.” Still, he believes better times are again coming -- and soon.

“At some point, we’re going to break through this and it’s going to start turning our way,” Mattingly said. “For us, it’s just a matter of getting some big hits. We haven’t been able to get that hit. I feel like we’ve hit some balls on the nose and not been rewarded, but that’s going to turn.”