ATLANTA -- The New York Mets showed what they can do when they have a healthy Steven Matz.

The left-hander looked sharp in his first start of the season, allowing one run in seven innings to help the Mets beat the Atlanta Braves 8-1 and sweep a day-night doubleheader on Saturday at SunTrust Park.

"We know he's capable of that," New York manager Terry Collins said. "Certainly, we saw a team that's swinging the bats very good. They got some bad swings against him. It just tells you what type of quality stuff he's got."

Matz (1-0) allowed five hits with one walk and two strikeouts in his first appearance since Aug. 14. The oft-injured southpaw opened the season on the disabled list with left elbow inflammation. He improved to 4-0 with a 2.70 ERA in five career starts against the Braves.

"I was able to locate the fastball away today," Matz said. "I didn't really have my greatest, sharpest stuff today, but I feel like I was able to execute pitches when I did and the defense behind me was playing great."

Collins said, "I've never seen Steven Matz try to strike anybody out. He's just got good stuff. He's around the plate. Kept it to 90-plus pitches today. That's the kind of outings we were going to get consistently."

The New York offense was boosted by a pair of home runs, a three-shot by Jay Bruce and a two-run pinch-hit homer by T.J. Rivera. The Mets have homered in 14 straight road games.

Atlanta starter Matt Wisler (0-1) was added as the 26th man to pitch on Saturday. He pitched six innings and allowed four runs on six hits with three walks and seven strikeouts. One of those walks came with two outs in the fifth inning and started New York's opening three-run salvo.

"He was good," Braves manager Brian Snitker said. "I liked what I saw there. He's making some progress. Early on it was really good."

The Mets added a run in the sixth when Wilmer Flores tripled and scored on a Travis d'Arnaud sacrifice fly. Flores was 4-for-5 in the nightcap and 6-for-9 in the doubleheader to up his average to .333.

The Braves scored their only run in the seventh when Dansby Swanson doubled and scored on Johan Camargo's single. The run ended a streak of 23 2/3 consecutive scoreless innings by New York starters.

The Mets made it 6-1 in the eighth inning when Rivera connected for his second homer of the season, a two-run shot, against reliever Eric O'Flaherty. It was Rivera's first home run since May 5 against Miami.

The Mets took a 3-0 lead in the fifth inning when Bruce hit a three-run shot, his 16th homer of the season. It was the second time Bruce went deep against Wisler this season, earlier touching him for a three-run shot.

"Had a hard time keeping it rolling and keeping the game in check because the kid (Matz) was really good," Snitker said. "I saw on his rehab he was up to 90 pitches and so he was ready to go and he's a tough ride anyway. We couldn't get anything going."

New York won the first game 6-1. Robert Gsellman pitched 6 2/3 scoreless innings and left fielder Yoenis Cespedes hit a grand slam, the fifth of his career, in his return from the disabled list.

Gsellman (5-3) allowed only three hits, with two walks and four strikeouts. It was the first time in 11 starts this season that he has not given up a run.

Sean Newcomb, considered Atlanta's top pitching prospect, made his major league debut. The left-hander (0-1) took the loss, despite allowing only one unearned run and four hits in 6 1/3 innings. He struck out seven and walked two.

NOTES: The Mets activated LF Yoenis Cespedes from the disabled list. He had been sidelined since April 28 because of a left hamstring strain. Cespedes admitted he was not 100 percent, but said, "I feel that I am ready to play." He started the first game, but not the nightcap. ... New York activated LHP Steven Matz for the second game of the doubleheader and sent INF Matt Reynolds to Triple-A Las Vegas. Matz has been on the disabled list all season because of left elbow inflammation. He was 0-1 with a 6.06 ERA in four rehab appearances. ... Atlanta sent RHP Jason Hursh to Triple-A Gwinnett to make room for LHP Sean Newcomb, who made his major league debut in the first game. ... Atlanta CF Ender Inciarte did not start the nightcap. He had played in the team's previous 59 games. ... Atlanta C Tyler Flowers has reached base in 21 consecutive games. ... New York SS Jose Reyes ended an 0-for-27 streak with a single in the fifth inning of the nightcap. ... Atlanta LF Matt Kemp was ejected by home plate umpire Phil Cuzzi at the end of the eighth inning.