Alcantara pitched shutout ball into the eighth inning in his second career start, Austin Dean drove in a pair of runs and the Marlins beat the Phillies 2-1 on Wednesday night.
Alcantara (2-0) allowed three hits, walked two and struck out six. His ERA, over 12 innings this season, dropped to 0.75.
"You're talking about a guy who can be a top of the rotation guy," Marlins manager Don Mattingly said.
The Phillies swept a four-game set from the Marlins from Aug. 2-5, and have lost 18 of 28 games since -- with no series wins in any of their last nine opportunities. They remained three games behind Atlanta in the NL East race, after the Braves wasted a 7-1 lead and lost 9-8 earlier Wednesday to Boston.
"We set out to win every baseball game," Phillies manager Gabe Kapler said. "And our pleasure or our disappointment hinges on how we perform, and not really what Atlanta's doing."
Derek Dietrich scored both Miami runs, the first when Dean hit into a fielder's choice in the second, the other on Dean's single to center in the fourth. Both of those runs were charged to Phillies starter Nick Pivetta (7-11), who gave up three hits and two runs in four innings.
"Their starting pitcher did a tremendous job," Pivetta said. "But at the end of the day, I was the guy who gave up two runs, so it's on me."
Drew Steckenrider allowed a walk and a single with one out in the ninth, but finished off his fourth save with a pair of strikeouts.
Alcantara walked Carlos Santana to lead off the game, walked Roman Quinn to lead off the eighth, and issued no other free passes. He was still reaching 98 mph in the seventh inning, then got himself out of a little situation in the seventh to preserve what was then a 2-0 lead.
Phillies catcher Jorge Alfaro, who had singled twice off Alcantara and had three hits on the night, got plunked in the left arm when a fastball from the Marlins rookie sailed up and in. Alfaro wasn't amused, took a long stare toward Alcantara as he walked to first.
But Alcantara wasn't rattled, and fanned Wilson Ramos on three pitches to end the inning with his 2-0 lead intact. The Marlins let him hit in the bottom of the seventh, then sent him back out for the eighth -- pulling him only after the walk to Quinn.
That runner didn't hurt Miami. Santana lined out to second baseman Starlin Castro, Quinn got caught 30 feet off the bag and the Phillies went from having the leadoff runner aboard to having the bases empty with two out.
"Everything was working tonight," Alcantara said.
Lewis Brinson had two hits for the Marlins, continuing his strong return after missing two months with a right hip injury. Brinson was hitting .154 when he got hurt; he's now up to .201, after going 8 for 18 since coming back.
Phillies: 3B Maikel Franco returned to Philadelphia to have his sore right wrist examined by a specialist. Franco is expected to rejoin the team later this week, and didn't play in any of the three games in Miami.
The Boston-Atlanta game was early Wednesday, which meant the Phillies could watch it in their clubhouse before taking the field in Miami. "We're focused on our club right now but we were certainly watching," Kapler said.
The Marlins and Phillies both met with a couple of the survivors from the Feb. 14 massacre at Marjory Stoneman Douglas High School before the game. Former Phillies star Jimmy Rollins signed some autographs, and players from both sides handed out bats and batting gloves as gifts.
Check out some of the nastiest pitches that stunned batters in the box including Adam Wainwright's curveball and Jordan Hicks' fastball.
Wei-Yin Chen will make his final home start of the season Friday in a year in which he has been dominant at Marlins Park.
The Tampa Bay Rays have even less room for error to keep their postseason hopes alive after dropping the opener of a four-game series against the Toronto Blue Jays in shocking fashion Thursday night in Toronto.
Angels catcher Francisco Arcia becomes the first player in MLB history to catch, take the mound and hit a home run in Los Angeles' 21-3 defeat in Oakland.
The American League East race is officially over and the New York Yankees can turn their focus toward more pressing matters.
The Red Sox celebrate their third-straight division title with a party in their locker room at Yankee Stadium.