Halladay (0-1), who struggled with a sore shoulder last season and had a difficult spring training, gave up five runs and six hits in 3 1-3 innings. The two-time Cy Young Award winner struck out nine, but dropped to 0-4 with an 8.00 ERA in his last seven starts against Atlanta.
The game was played in a steady drizzle, but the conditions hardly affected Paul Maholm (1-0), who allowed six hits in 5 2-3 scoreless innings. He struck out six and walked one.
Gattis led off the fourth inning of his first major league game with a drive to left.
The Phillies were just 1 for 11 with runners in scoring position.
NATIONALS 3, MARLINS 0
WASHINGTON -- Left-hander Gio Gonzalez homered, providing all the offense necessary to back his six scoreless innings, and Washington picked up another win.
Gonzalez (1-0), a 21-game winner in 2012 who finished third in NL Cy Young Award voting, allowed only two hits, along with five strikeouts and two walks.
His solo shot to left field off Kevin Slowey (0-1) came with one out in the fifth. Slowey gave up one run and four hits in 5 1-3 innings.
Rafael Soriano got his second save, completing Washington's second straight shutout of the Marlins.
METS 8, PADRES 4
David Wright added an RBI double in a game that began with a wind chill of 32 degrees.
Making his 11th career start and fifth at home, the 24-year-old Harvey (1-0) didn't allow a baserunner until Everth Cabrera singled to center field leading off the fourth.
Richard (0-1) gave up eight runs in 4 1-3 innings.
PIRATES 3, CUBS 0
PITTSBURGH -- Wandy Rodriguez allowed just two hits over 6 2-3 innings and Pittsburgh earned its first win of the year.
Jason Grilli, promoted to the closer's role in the offseason, worked the ninth for his first save.
Rodriguez (1-0), acquired in a trade deadline deal with Houston last July, struck out six and walked one in a continuation of his strong spring.
Edwin Jackson (0-1) gave up two runs in five innings but lost to the Pirates for the first time in seven career starts. The Cubs produced just two singles and only put a runner on third once.
ROCKIES 7, BREWERS 3
The Rockies took two of three under new manager Walt Weiss in the season-opening series at Miller Park.
Nicasio (1-0) allowed two runs and seven hits for his first win since last April 30, when he beat the Los Angeles Dodgers. Winless in the next five starts, he went down with a season-ending knee injury on June 2.
Wily Peralta (0-1) gave up four runs, including Rosario's two-run homer.
Rickie Weeks hit a solo shot for Milwaukee.
REDS 5, ANGELS 4
The Reds and Angels have split the first two games of the first interleague series to open a season.
Votto's first hit of the season off left-hander Scott Downs (0-1) deflected off the glove of first baseman Albert Pujols and rolled into the outfield, allowing Shin-Soo Choo to score from second base. Choo reached when he was hit by a pitch and advanced on a sacrifice.
Votto had been 0 for 6 heading into the decisive at-bat.
Left-hander Aroldis Chapman (1-0) walked one in the ninth, throwing a 99 mph pitch that hit the backstop screen.
Copyright 2013 by The Associated Press
This story is from ESPN.com's automated news wire. Wire index
MORE MLB HEADLINES
- Tanaka apologizes to Yanks, fans for injury
- CarGo back with Rockies after long DL stint
- D-backs reinstate slugger Trumbo from DL
- Reds' Latos exits early with back spasms