Harris, 32 and in his first season with the Mets, is 4-for-10 with a homer this season, and he's scheduled to start Wednesday against the Phillies' Joe Blanton in the 7:05 p.m. ET start at Citizens Bank Park.
Scott Hairston started in left on Tuesday.
"I thought about it and thought about it, and actually Sandy and I have talked about it," Mets manager Terry Collins said. "It's pretty hard to take him out of the lineup right now. No disrespect to Lucas, but when someone's as hot as Willie is, it's pretty hard to put him on the bench."
Harris isn't the only Mets bench player to contribute in the early days of the season. Chin-Iung Hu and Daniel Murphy have both seen playing time, and Collins' intention is to get his reserves as much action as possible.
"I truly believe that your role players, they have to get four at-bats at some time in a game," Collins said. "When you use them to pinch-hit, if they don't get some consistent at-bats, they can't come off that bench and give you much. So I'm going to try to make sure that each week, those guys get a game in sometime."
Showing some early energy on the road that the Mets' displayed little of last season, New York took the first game of the three-game set Tuesday night, 7-1.
Blanton makes his 2011 debut after being subjected to trade rumors in the offseason, mostly thanks to the Cliff Lee signing. Blanton responded with a strong spring: he threw more innings than anyone in Phillies camp with 31, and he pitched effectively, too. He walked just four, struck out 18 and posted a 3.19 ERA.
Mike Pelfrey makes his second start of the year for New York on Wednesday after letting up five runs to the Marlins in an Opening Day loss. Pelfrey's rarely fared well at Citizens Bank Park: in his career, he's allowed 23 runs in 25 1/3 innings, a span of five outings.
Mets: Good news about Paulino
General manager Sandy Alderson said Tuesday that backup catcher Ronny Paulino has shown improvement from a blood disorder and may not need to spend time on the disabled list.
Paulino has four games remaining on a suspension handed down last season for a positive performance-enhancing substance test. After he finishes serving it this weekend, the Mets must decide whether to activate Paulino or place him on the DL, which would sideline him until at least late April.
Phillies: Howard changes pace
Historically, Ryan Howard's fared the worst at the plate in April. Not this go around.
The slugging first baseman entered Tuesday night 7-for-13 with a home run, six RBIs and three strikeouts.
"He's done a good job so far. Much better," manager Charlie Manuel said of Howard's approach at the plate. "He's supposed to zone the ball. He did a pretty job of it. He's been patient. He's been working on getting good balls to hit."
The Mets were 5-17-4 in road series in 2010. Another win against the Phillies in the next two games gives them two straight road series wins to open the year. ... The Phillies were dominant in night games last season, going 70-41 and posting the Majors best win percentage: .631. Only Texas won more night games, 71, but the Rangers had a lower win percentage, .602.