The Marlins and right-hander Josh Johnson are in town for the second game of the three-game set in Philadelphia, where Miami took the opener on Monday, 6-2.
The two National League East rivals have a scheduled day off on Tuesday before resuming the series Wednesday night.
"If we're a rivalry, that means we're playing good," Marlins manager Ozzie Guillen said. "I think they are talking because everything is new. People are going to talk about you when you have a great ballclub. We do. Hopefully we play the way we look."
Johnson is 4-0 with a 1.87 ERA in six games (five starts) at Citizens Bank Park. Halladay, meanwhile, is 20-8 with a 2.31 ERA in the Phillies' home stadium.
The Marlins' ace took the loss on Opening Night against the Cardinals, while Halladay earned a victory in his first start of the year.
"He was a different guy than in Spring Training, I can tell you," Phillies catcher Carlos Ruiz said after Halladay's first start. "In the season, as you can see today, that's Roy. ... He was definitely on [Thursday]. It's like he hit a switch. He turned it on, and he was ready to go."
Johnson allowed three runs on 10 hits (tied for a career high) with two walks and four strikeouts over six frames against St. Louis. But because of two off-days, he will be pitching Wednesday on seven days' rest.
"It feels weird. It feels like I haven't thrown in forever," Johnson said. "I threw my bullpen [session on Sunday], and [Monday] would have been my normal day to pitch. It feels a little weird. I did get about a day-and-a-half break. On the [Friday] off-day, I didn't do anything. I hadn't taken a full entire day off [since] before Spring Training."
The Marlins are hoping to find more opportunities to rest Johnson throughout the course of the year. His 2011 campaign was shortened by right shoulder soreness.
"I want the same thing," Johnson said. "I know we're on the same page. They said they didn't want to skip anybody unless somebody needed an extra day. They said that from the beginning, we're going to go with all five starters, no matter the off-days in between there."
The Phillies won 12 of the 18 meetings between the two teams in 2011, and seven of nine in Philadelphia.
Phillies: Rollins off to the races
Shortstop Jimmy Rollins, who has been helping to fill the void left by the absence of Chase Utley and Ryan Howard by batting third this season, has provided a spark in the middle of the Philadelphia offense. He was 2-for-4 with a stolen base on Monday, and now has a hit in three of the Phillies' four games.
After starting his Major League career on an 0-for-12 skid, Freddy Galvis picked up his first big league hit in the seventh inning Monday with a one-out, two-run double.
After Phillies starters through the first three games of the season (Halladay, Cliff Lee and Vance Worley) combined to allow just two earned runs in 20 innings (0.90 ERA), Cole Hamels exited Monday after surrendering four runs (three earned) on eight hits in 5 1/3 innings.
Marlins: Power from an unlikely source
Omar Infante, who has not hit more than eight homers in a season since 2005, has hit three in as many games for the Marlins. Monday was the seventh multihomer game of his career, and the first since Sept. 9, 2011, in Pittsburgh. Infante hit seven long balls last year.
After scoring one run in their first two games, the Marlins have averaged 6.33 runs per game over their past three (two wins, one loss).
"We've just got going," Johnson said. "Especially early on. It seems like we were hitting balls hard right at people, and they're blooping balls in and rollers are going through the infield. It seems like that's how it's going."
The Phillies dropped their first home game of the season on Monday after finishing the 2011 campaign 52-29 (.642) at Citizens Bank Park, tied for the second-best home mark in baseball with the Yankees (the Brewers were 57-24).
Guillen will return to Miami on Tuesday's off-day for a 10:30 a.m. ET news conference during which he plans to address the media and the Cuban community regarding the comments he made about Fidel Castro in a Time Magazine article.
Monday was Philadelphia's first game of the season that was not decided by one run.