Unable to repeat his delivery and consistently throw strikes, Miller was tagged for four runs in three innings in his final start of the season.
Brooks Conrad's three-run homer in the third inning and Derek Lowe's successful outing on short rest lifted the Braves to a 5-1 victory over the Marlins on Wednesday at Turner Field.
Miller's final start of the season was another reminder that the left-hander has a ways to go in terms of getting consistency in his delivery.
"The way it started and the point I'm at right now, it's not the way I wanted it to go," said Miller, who is now 1-5. "I think I'm getting closer. I've been saying that for a long time. My stuff was good today. My velocity was good. My changeup was good. I didn't throw too many breaking balls to all those righties. I threw a couple of good ones later in the third inning.
"But [I threw] far too many balls today, and I've just got to find that consistency in the strike zone."
The Braves completed their three-game sweep, strengthening their position to secure the National League Wild Card.
"You know what: Those guys are hungry. They can taste it," said Chad Tracy, who had three of the Marlins' nine hits. "You've got to tip your hat to them."
For Florida, Wednesday was yet another stifling afternoon.
The Marlins concluded their final road trip by going 1-6, including four straight losses. For the season, they were 39-42 away from Sun Life Stadium.
Now 77-81, the Marlins will have to sweep their four-game home series with the Pirates, beginning Thursday, to finish an even .500. But for the first time since going 71-91 in 2007, Florida will have a non-winning season.
Florida's offense managed five runs over the four-game losing streak.
"There was no offense on this road trip," manager Edwin Rodriguez said.
In the seven games on the trip, the Marlins scored 14 total runs.
"There was no offense. We scored what, 14 runs? In the last four games, [five] runs in four games," Rodriguez said. "There were no runs. The clutch hits never came. Hopefully, going back to Miami -- in those last four games, hopefully, we can start getting those clutch hits."
Lowe (16-12) pounded the zone in 5 2/3 innings, striking out nine while giving up one run. Of his 99 pitches, 63 were strikes.
Miller's last start of the season was again a struggle to throw strikes. The lefty walked four in three innings, and 43 of his 77 pitches were strikes.
Miller's lone win this season was against the Braves in Miami on Sept. 3, when he gave up one run on seven hits with three walks in five innings.
"Miller is hard. He'll walk a couple and then he will make some pitches," Braves manager Bobby Cox said. "Same thing down in Miami the last time we faced him. It was walk, walk, walk and then we'd line out somewhere and end up with nothing."
In the first two innings, Miller was able to work out of trouble with runners in scoring position. But in the third, the mounting number of baserunners caught up to the left-hander.
Atlanta broke through for four runs, with the big blast being Conrad's three-run homer.
A pair of one-out walks issued by Miller set up the big inning. With two outs, David Ross delivered an RBI double, and Conrad followed with his eighth shot of the season.
Unless Miller is used out of the bullpen in the final series with the Pirates, he will have walked 26 while striking out 28 in 32 2/3 innings.
Boosted by the four-run third inning, Lowe was able to toss 5 2/3 innings on three days' rest. In back-to-back games, the Braves picked up a solid start from a veteran going on short rest.
Tim Hudson gave up one run over six innings in a no-decision Tuesday.
"We did exactly what we had to do. We played three very strong games against Florida," Lowe said.
The Marlins cashed in on Lowe in the sixth inning, scoring on Mike Stanton's two-out RBI single. A single by Dan Uggla and a two-out single by Tracy set up Stanton's 53rd RBI.
Lowe exited to a nice ovation as Peter Moylan prevented any further damage by striking out Brad Davis.
"There's a reason why they're going on short rest, because they're the heart and soul of that pitching staff," Tracy said. "They're expected to go out there and earn that paycheck, and they did."
Joe Frisaro is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.