Schwarber had two hits, but the rest of the Phillies managed just three and fell 6-2 to the New York Mets in the series opener.
Schwarber's homer came off Kodai Senga, who was a surprise Game 1 starter for New York after throwing just 5 1/3 major league innings all season.
"It was hard to map out because we didn't know what we were getting out of Senga, to begin with," Mets manager Carlos Mendoz said. "He was really good, by the way. Other than that pitch that Schwarber took him deep, he was really good."
Schwarber, who hit 38 home runs in the regular season, including 15 from the leadoff spot, has 21 career playoff home runs in 66 games. That ranks him fourth behind Manny Ramirez (29), Jose Altuve (27) and Bernie Williams (22).
Jimmy Rollins and Derek Jeter each had three career leadoff home runs during the playoffs.
The next game takes place at Citizen's Bank Park just after 4 p.m. Sunday.
RELATED: Phillies to host Mets at Citizens Bank Park this weekend for start of NLDS | What you need to know
Fan Reactions
Across Philadelphia, fans told Action News they were disappointed after a rough loss.
"The big stars didn't show up. It's really a shame for Wheeler, too -- pitched such a great game. Pitched his heart out," commented Jack Larson from Feasterville.
Many said it was all the more upsetting since the team had such a strong start.
"Right off the rip I thought it was awesome. Schwarber right in the first inning. Everybody is getting excited everywhere in Philadelphia," recalled Michael Olsen from Haddon Township.
But soon enough, Phillies fans say they knew the game was taking a sour turn.
"Horrible -- I saw it coming. They didn't get any runs, Wheeler was pitching fantastic. Once they went to the bull pen, the Mets were gonna wake up and that's what happened," said Fran Whitton from Harleysville.
With so much riding on the Phillies, fans are anxious for the future -- but optimistic.
"It's a must-win, if the bats don't wake up this is gonna be a short series for the Phillies," said Whitton.
"Very disappointed, but you know something? We're gonna come back. They'll come back. We had a great team all year, we're gonna win this series," added Pat Burns from Newtown Square.
The Associated Press contributed to this report.